Systematic review and evolution of the early Cytheruridae (Ostracoda)

A review of the literature on the taxonomy of Triassic and Early Jurassic cytheracean Ostracoda reveals that the validity of many genera is questionable. A number of studies of the Triassic microfaunas from eastern European sequences have, in particular, obscured the true generic and suprageneric classification of many ostracod taxa. The present study concentrates on the diverse extant cytheracean family the Cytheruridae, whose origins are in the earliest Mesozoic–latest Palaeozoic, but it is clear that many contemporary cytheracean families present similar problems. This review clarifies the previous taxonomic confusion and obfuscation by demonstrating that many of these genera are spurious having been erected on specific rather than generic morphological criteria. Many of them are best accommodated within the extant genus Eucytherura Müller, 1894. Most of the cytherurid genera known from the Liassic deposits of NW Europe can be traced back to these Triassic assemblages. In considering the origin and earliest evolution of the Cytheruridae, we note that some Triassic taxa share characteristics typical of both the Cytheruridae and the Bythocytheridae and it is suggested that the former may have arisen from the latter family during the latest Permian or earliest Triassic. We also note that the palaeoenvironmental interpretation of many of the Triassic deposits is brackish-water, marginal marine.


INTRODUCTION
The family Cytheruridae G. W. Muller, 1894 is one of the most diverse extant families of ostracods with a fossil record extending back to the Early Mesozoic or possibly the latest Permian. Today they are almost exclusively marine, although there are some euryhaline species. During the Cenozoic the family was almost equally diverse in shelf and deep-sea environments. Mesozoic cytherurids seem to have been largely confined to shelf depths but shallow, brackish-water taxa are also known. This paper is limited to a consideration of Permian, Triassic and earliest Jurassic taxa.
In an attempt to establish the phylogenetic origin of the cytherurids we have re-evaluated the available published descriptions of Triassic marine and marginal-marine cytheracean taxa in a literature search of global scope. In this study we have considered a large number of genera and species, many of which are discussed here. We have found it necessary to synonymize a number of genera and also entire families as Whatley & Moguilevsky (1998) did in a similar study of the Limnocytheridae. Within these Triassic assemblages we recognize some of the earliest representatives of the Cytheruridae. With some taxa we have experienced difficulties in determining their familial status. This is only to be expected early in the adaptive radiation of a superfrlmily and that of the Cytheracea is no exception (Whatley & Stephens, 1976;Whatley, 1988).
The first major evolutionary radiation within the Cytheruridae is recognized to have taken place during the latest Triassic to Early Jurassic (Whatley et al., 1993), with some of these newly established genera surviving to the present day (e.g. Cytheropteron. Eucytherura). A large number of post-Palaeozoic cytheracean ostracod families can be traced back to the earliest Mesozoic, following the final extinction of many 'palaeocopid' ostracods by the close of the Permian (Whatley & Stephens, 1976). Some authors signally failed to recognize that many of these early Cytheracea belonged to pre-existing post-Triassic genera and placed them in a series of spurious new genera. This is particularly true of the marine and euryhaline assemblages of Central, East and SE Europe. One of the consequences is that these 'new' genera appear to be stratigraphically restricted to the Triassic. Furthermore, many of the new genera have been erected on the basis of what we regard as specific characteristics and this is supported by the observation that many of them are mono-specific and, in some cases, were erected on a single specimen. The true suprageneric position of these taxa has, therefore, been obscured and the phylogenetic significance of these assemblages has only recently become apparent. The problem is compounded by the fact that these new taxa were placed in new families that were also stratigraphically confined to the Triassic. Many Liassic species, as demonstrated below, were also placed in new genera restricted to the Early Jurassic and we have synonymized a number of them.
The Late Palaeozoic demise of the 'palaeocopids' and other ostracod groups resulted in the emergence of typical Mesozoic assemblages, many of which have not previously been recorded in pre-Jurassic sediments. It would appear that their 'absence' from Triassic sediments was an artefact caused by misidentification and mis-interpretation. We believe that it is now possible to establish the antiquity, if not necessarily the origin, of the Cytheruridae within these Triassic assemblages.
The Cytheruridae belong to the Superfamily Cytheracea (Order Podocopina, Ordovician to Recent) which dominate most post-Palaeozoic marine assemblages. The Cytheracea are characterized, among other features, by a vertically aligned row of four (rarely three or five) adductor muscle scars. The majority of Palaeozoic ostracods are distinguished by the possession of a sub-circular, irregularly arranged group of between 10 and 100 individual muscle scars, the only known Palaeozoic cytheracean ostracods are the Perniianidae, the Limnocytheridae (Whatley & Moguilevsky, 1998) which are non-marine, and the marine Bythocytheridae. The Permianidae are characterised by a vertically aligned row of three and the Bythocytheridae by five adductor muscle scars, while the Limnocytheridae like virtually all other Cytheracea have four vertically aligned adductors. It is our contention that the Bythocytheridae were the root stock which, during the Late Palaeozoic or Early Mesozoic interval, gave rise directly or indirectly to all other Cytheracea and that one of the earliest recognizable cytheracean families is the Cytheruridae.
Conventionally, three subfamilies are recognized within the Cytheruridae: the Cytherurinae, the Cytheropterinae (Hanai, 1957) and the Paracytherideinae (Mandelstam, in Orlov, 1960) (although some authors accord the latter separate familial status while others would include additional subfamilies such as the Late Cretaceous to Recent Oculocytheropterinae Bate &Coleman, 1975 andthe Jurassic to Recent Eucytherurinae Puri, 1974. The present authors contend that the majority of cytherurid species identified in the Triassic belong to the Cytherurinae while some are certainly, and others possibly, members of the Cytheropterinae. The family is known to be well established by the Early Jurassic. The Paracytherideinae are believed to have their earliest record in the Cretaceous and are not considered further in this study. Unfortunately, many of the specimens figured in the literature on Triassic ostracods are often poorly illustrated andjor poorly preserved. As an additional complication, it is now clear that few of the types or specimens illustrated by Kozur and his colleagues were deposited in accessible collections and many are now certainly lost (Kozur, pers. comni.). Therefore, it is not possible to re-examine the majority of the type specimens and we are left with only the original illustrations, type descriptions and personal communications with the original authors. There are very few descriptions of taxonomically important internal features such as adductor muscle scars or hingement. Nevertheless, we believe that it is possible to draw important conclusions based on external features and gross carapace morphology. Hingement in Early Mesozoic cytheracean ostracods is generally lophodont, more rarely merodont. In the following sections we discuss the validity of many Permian to Early Jurassic genera. In many cases the type material is lost or was never curated. A complete taxonomic revision would warrant re-collection from all of the type localities combined with an exhaustive search of museum collections. We have chosen not to figure the few taxa that are available since they are already well illustrated in the literature. We have fully referenced the type description of each taxon discussed, since only through observing the original illustrations can the taxonomic problems be fully appreciated. We hope that this paper will stimulate further research on an important period in ostracod evolution It is our opinion that many of the species recorded from the marginal-marine and marine Triassic deposits world-wide can easily be accommodated within already existing genera originally described from younger strata. Many previous taxonomic studies have obscured true evolutionary relationships by not distinguishing between generic and specific criteria. We have adopted the taxonomic philosophy outlined by Whatley & Ballent (1996) in which generic characters are of kind while specific characters are of degree. Clearly there is scope for future research into the Early Mesozoic development of cytheracean ostracods, a fundamentally important period in their evolution.

SYSTEMATIC DISCUSSION
What follows, in alphabetical order, is an evaluation of a number of Late Palaeozoic-Early Mesozoic genera that are possible candidates for inclusion within the Cytheruridae. Some are accepted as members of the family while others are rejected. Genera which we consider valid, whatever their family, are given in titulo underlined and are diagnosed, those that we consider valid but which only occur in sediments younger than Early Jurassic are not diagnosed. The family to which we believe the valid taxa belong is also given and modern diagnoses of the Cytheruridae and its two relevant subfamilies are also presented. LV, left valve; RV, right valve. The following convention is used to describe ostracod size (in adult specimens) Very small < 0.4 mm Small 0.4-0.5 mm Medium 0.5-0.7 mm Large 0.7-1 .0 mm Very large > 1 .0 mm

Suprageneric classification
Class Normal pore canals ranging from simple (the most common) to primitive sieve-type. Radial pore canals rather few, simple, often sinuous and with false canals. Mainly avestibulate but small vestibula may be developed at either end. Inner margin usually regular but may be very irregular. Frontal scar ovate, reniform to v-shaped and sometimes subdivided. Hinge lophodont or merodont, often strongly modified and sometimes secondarily adont, very rarely pentadont.
Smooth to strongly ornamented with ribs, tubercles, etc. Vestibula small or absent. Hinge as for family but never adont. Inner margin parallel to widely divergent. Radial pore canals often long, sinuous with false canals. Eye tubercles frequently well developed in ornate taxa Subfamily Cytheropterinae Hanai, 1957 Diagnosis. Carapace subovate, with dorsal margin often rounded, to subquadrate and sub-rectangular. Feebly ornamented, smooth to punctate or reticulate. Usually strongly alate or tumid ventro-laterally. Small vestibula usually present. Hinge usually antimerodont but often modified. Without eye tubercles.

Generic classification
Genus Blomella Kozur, 1973?1956Mandelstam et al.: 120. Type species. Speluncella sulcata Kozur, 1968b (p. 509, pl. 1, figs Diagnosis. Carapace small to medium size, smooth, LV > RV. Ventral margin straight; anterior, dorsal and posterior margins form a highly arched outline in lateral view. Ventral margin flat and extended laterally into distinct flanges. Hinge short, lophodont. Remarks. The type species, Blomellu sulcuta, was originally assigned to Speluncdla Schneider (in Mandelstam et al., 1956) which Whatley & Moguilevsky (1998) place in the Limnocytheridae, Timiriaseviinae. B. sulcata is at least outwardly similar to members of the Timiriaseviinae. The type species is somewhat cytheropterine (reminiscent of Modern deep-sea taxa such as Cytheropteron testudo) but Kozur (pers. comm., 1997) states that the genus was recovered from brackish water sediments and it is very rare for fossil or Recent members of Cytheropteron or its allies to occur in environments of reduced salinity. Although Whatley & Moguilevsky (1998) did not include Blomella in their 3,8,23,24,[27][28][29]. review of the Limnocytheridae, it is probably a valid member of that family and not a cytherurid. Blomella may be a junior synonym of Speluncella but for the time being we accept it as a valid taxon but not a member of the Cytheruridae.
Speluncella.? ampelsbachensis, from 'probable marine Late Norian sediments' (Kozur, pers. comm., 1997), was described by Kozur & Bolz in the same publication (Kozur, 1971, p. 46, pl. 3, figs 6-7) and is probably congeneric. A number of similar species are also present in the Early Jurassic sediments of the Mochras Borehole, Wales (Boomer, 1989 and unpublished data) and these almost certainly constitute a distinct group within the Cytheropterinae. It is our opinion, therefore, that the genus Citrellu ranges from the Late Norian to the mid-Bathonian and possibly to the Tithonian (Pokorny, 1973 Remarks. The genus Cytheropteron has been reported in Triassic assemblages as two distinct subgenera, Cytheropteron (Cytheropteron) I Cytheropteron (Stykella) ; the nominative subgenus has its oldest certain record in the Toarcian (Cythrropteron alufustigatum Fischer, 1962, ,falcferum Zone, Mochras Borehole, Great Britain; Boomer, 1989). The species Cytheropteron? triassica described by Kozur (1971) is almost certainly not a valid member of that genus. Bate & Coleman (1975) erected the subfamily Oculocytheropterinae to incorporate the eyed Cyther-opteron-like species, i.e. the Late Cretaceous to Recent Oculocytlieropteron Bate and they included the Liassic genera Rutlandella and Wellandiu (see below). In the following sections we synonymize the latter two genera with Eucytherura which is accommodated within the Cytherurinae. The Oculocytheropterinae are not considered further here. Lobosocytheropteron is based solely on the fact that species such as C. alatuni Sars, 1866 have a bend in the median element of the hinge. We do not consider this to be a generic characteristic.
Remarks. The subgenus Infiacytheropteron (originally erected as a monospecific Early Cretaceous taxon) was differentiated from Cytheropteron on the basis of hingement which was said to consist of a smooth bar in each valve, produced by the enlargement of the selvage and valve margins. This may have been erroneously described from a juvenile specimen, no internal views were figured in the type description although the duplicature was described as narrow. A number of Liassic species have subsequently been assigned to this subgenus (see Bate & Coleman, 1975;Knitter, 1983) an assessment which appears to be based largely on external characteristics, the status of this taxon is at best questionable and we consider it to be a junior synonym of Cytheropteron.
Remarks. This was erected as a subgenus of Cytheropteroii to accommodate a single species. The straight hinge line precludes its inclusion in Cytheropteron. It is described as having a 'hemimerodont' hinge and from the type figures it clearly possesses an eye node, a caudal process and a ventro-lateral extension which terminates posteriorly in a small blunt spine. Its shape disqualifies it for inclusion within Aversovulva Hornibrook, 1952or Oculoc~j~theropteron Bate, 1972. In all characteristics it clearly belongs within Eucytherura Muller.
Genus Detterinania Sohn, 1987 Type species. Dettermania truncata Sohn, 1987 (p. 11, pl. 7, figs 4-1 5). Remarks. Sohn (1987) described the type species of Dettermania together with two similar species which he assigned to Covracythere (Gramm, 1975) from the marine Triassic deposits of Alaska. All three species are morphologically similar and it is possible that they are congeneric. The genus Covracvthere is, without doubt, a bythocytherid (possessing five adductor muscle scars) and was originally described along with two other bythocytherid genera, Racevetina and Acvocariu, from the Far East of the Former Soviet Union (Gramm, 1975). All three species figured by Sohn possess median sulcii and straight dorsal margins, indicating that they may belong within the Bythocytheridae. However, without supporting details of the muscle scars, any such assignments n--!ut remain uncertain.
N o details of the muscle SLaib ur hingement of Dettermuniu are available. The carapace shape and external morphology is distinct and strongly suggests that it is congeneric with Mockella Bunza & Kozur, 1971, as is Hasibuanu Kristan-Tollmann (in Kristan-Tollmann & Hasibuan, 1990; see below). Dettermania differs slightly from Mockella in that it lacks secondary intercostal ornament, however, we conclude that this is a specific character and therefore Dettermaiiia is a junior synonym of Mockrllu.
Genus Eocythereis Anderson, 1964 Type species. Eocythereis vertebralis Anderson, 1964 (p. 145, pl. 13, figs 79-80). Remarks. Anderson (1964) placed this genus in the Trachyleberididae which has its origins in the Early Cretaceous (Whatley et al., 1993). Recent examination of the type material (originally erected on a single carapace), from the Rhaetian, Cotham Beds of Warwickshire, Great Britain (Anderson, 1964) Ayress et al. (1995). Remarks. A long-ranging genus originally described from Recent sediments in the Gulf of Naples (Muller, 1894) although the type species, Eucytherura complexa (Brady, 1867), was oiily later designated by Alexander (1936). The genus is distinguished from most other cytherurid taxa by its quadrate carapace in lateral view, which is only moderately inflated in dorsal view and the dominance of reticulate ornamentation. However, up to three longitudinal ribs (generally dorso-median or median and ventro-lateral in position) may also be present. Most species possess a strong tubercle or spine at the posterior apex of the ventro-lateral rib which itself may become quite inflated. Many species are characterized by the presence of a strong eye tubercle but Cenozoic and Recent species which live in deep water are blind. We prefer to include Eucytherura within the Cytherurinae. discussion of the status of the subfamily Eucytherurinae can be found in Maddocks & Steineck (1987).
We consider Eucytherura to be a senior synonym of the following Early Mesozoic taxa (with the family they were originally assigned to, if available): Eocythereis (Trachyleberididae), Gramannicythere, Graminella, Grammicythere, Movschovitschia, Nanacythere (Domeria) (Cytheridae), Nanacythere (Goniocythere), Parutrachycythere, Rutlandella (Oculocytheropterinae), Wellandia (Oculocytheropterinae) and a number of Early Jurassic species assigned by some workers to Acrocythere (e.g. Michelsen, 1975). All the above spurious taxa, and others erected in the subsequent Mesozoic and Cenozoic are, in our opinion, the product of confusing generic and specific criteria. Griindel (1975) claimed that all Mesozoic Eucyflzeruru are vestibulate, however, our own observations do not support this statement. We consider the subgenus Eucytherura ( Vesticytlzerura) (Griindel, 1964) to be an unnecessary taxon.
Genus Fulloticythere Kozur et al. 1974. Type species. Falloticythere muldcrae Kozur et al. 1974 (p. 36, text figs 19a,b,d;pl. 2, figs 9-13). Remarks. This genus was placed in the Cytherissinellidae by KOZLIS et al. (1974) and this family has now been subsumed within the Limnocytheridae (Whatley & Moguilevsky, 1998). Kozur et al. commented on the presence in the type species, Fulloticyflzere niulderae, of an antero-ventral node and an antero-median to mid-anterior node, these features produce a mid-valve sulcus which is found in most bythocytherid and many limnocytherid taxa. The hinge was described as lophodont with weak terminal teeth. The type species occurs in salinities ranging from marine to continental hyposaline (Kozur, pers. comm.).
Although possibly a cytherurid, and without internal details it is impossible to be sure, we believe that the weak hingement and carapace shape are best accommodated within the Bythocytheridae, and Falloticytlzere may be a junior synonym of Monocerutina Roth, 1928. As with Covrac,gthere a number of Triassic cytheracean taxa appear to share common bythocytherid and cytherurid characteristics, indicating the possible origin of the Cytheruridae from bythocytherid stock in the Late Permian or earliest Triassic.
Genus Grumannicythcre Griindel, 1975. Type species. Loplzodentina,? hachi Gramann, 1962 (p. 195, fig. 2; Remarks. This is synonymous with Nunacythere (Goniocythere) Michelsen, 1975 which was published a few months later. The genus comprises a few, mainly Pliensbachian, cytherurid species with a strongly angular development in the lateral primary ribbing. The taxonomic status of both Nunacythere (Domeria) Herrig, 1969 and Nanacytliere (Nanacythere) are discussed below. We consider Grumannicytlzere and, therefore, Nunucytliere (Goniocythere) to be junior synonyms of Eucytherura. Although possibly a valid taxon (and we consider it as such in the summary table), the lack of descriptive and illustrative material makes it impossible to provide a meaningful diagnosis at this time.

Remarks.
Granzmicythere replaced Grammella Kozur, a junior objective homonym of a bryozoan. The original publication also mis-spelt the name as Gramella. The type species possesses a straight to slightly convex dorsal margin and reticulate lateral surfaces with a ventro-lateral rib, it clearly belongs within the Cytherurinae and seems best accommodated within Eucytlierura, although no eye-spots were recorded (many modern species of Eucytherura lack eyes, especially those which occur in deep pl. 4, fig. 3). water). Kozur (1971) states that it is closely related to Lutkcviclzinella Schneider (in Mandelstam et a)., 1956) a genus which Whatley & Moguilevsky (1998) have shown to be a limnocytherid. However, on the basis of the very poor illustrations of the type species of Grammicytliere it is difficult to observe any points of similarity with Lutkevichinella. Notwithstanding this, we believe the genus to be another junior synonym of Eucytherura.
Genus Gruendelirytlzere Kozur, 1971 Type species. Gruendelicythere ampelshachensis Kozur & Bolz n. sp. in Kozur, 1971 (p. 24, pl. 6, figs 6-10). Diagnosis. Carapace small, rather elongate, dorsal and ventral margins straight converging slightly posteriorly. Posterior and anterior margins rounded in lateral view, compressed in dorsal view. Lateral surface bears marked reticulate nodes and sulcii, the largest of which are in the mid-to postero-ventral region. They do not extend beyond the dorsal margin in lateral view. Ventral surface flat and broad. Hinge probably lophodont.

Remarks.
The type species is a very small cytherurid and, although it resembles Eucytherura, it differs from most species of that genus in possessing particularly large nodes and tubercles for such a small ostracod. It has a slightly produced posterior with compressed anterior and posterior margins. Kozur (1 971) refers to the similarity of its noding to Judahrlla Sohn, 1968 but the distribution and nature of the noding in the two genera is quite different, as is the carapace outline (most species of Judahella have well developed nodes which extend beyond the dorsal margin) and the similarity is probably convergence. In the shape of the carapace and the distribution of nodes it differs significantly from the nodose Liassic cytherurid Trachycythere Triebel & Klingler, 1959. There are superficial similarities with Cretaceous and Cenozoic genera, such as Cliapmanicytlzerura Weaver, 1982, Hemingwuyella Neale, 1975 and Purahemingwayella Dingle, 1984 but Gruendelicythere differs sufficiently from all the above comparitors for us to consider it valid. A species assigned to this genus has been described from the Late Permian of northern Hungary (Kozur, 1985 Remarks. The type species possesses a well-developed pair of diagonal, lunate ribs with weak intercostal reticulation; a poorly developed eye-spot is also present. The carapace has a straight dorsal and highly convex ventral margin and in this respect is very similar to Dettermania in lateral outline. However, it lacks the median sulcus of that genus. Kristan-Tollmann (in Kristan-Tollmann & Hasibuan, 1990) noted that Hasibuana differs from Dettermania in possessing an eye-spot, and antero and posteromarginal ribs. We consider these differences to be of specific rank only and, therefore, that Husihuuna, like Dettermania, is a junior synonym of Mockella based on carapace shape, size and distribution of major ribs.  Sohn, 1968 (p. 15, pl. 3. figs 2 0~ 21). Diagnosis. Small, oval to triangular in lateral view. Dorsal margin straight, ventral margin convex, strongly so in some species. Anterior margin flat to broadly rounded. Greatest length near dorsal margin, greatest height near anterior margin. The valves are sometimes smooth but more commonly reticulate and bear a number of distinct swellings or nodes which are consistently developed within species. In many species these nodes extend beyond the dorsal margin in lateral view. There may also be a longitudinal rib present ventro-laterally. Hinge merodont. Muscle scars a vertically aligned row of four.
Remarks. Sohn (1968) originally placed this genus in the Palaeocopida (Superfamily unknown) and in a new family, the Judahellidae. Sohn discussed its possible relationship to a number of genera such as Cornigella Warthin, 1930 and Trachycythere. We consider Judahella to be a cytheracean, and almost certainly a cytherurid, characterized by a small, straighthinged carapace with 3 4 large dorsal tubercles extending beyond the dorsal margin. Kozur (1968b, p. 502) noted that Casachstanellu scungayica Schleifer, 1966, the type species of that genus, is a brackishwater form related to Judahella. Kozur (l970a) later considered Juduhella to be a junior synonym of Triassinella Schneider (in Mandelstam et a/., 1956), however, Whatley & Moguilevsky (1998) placed Triassinella in the Limnocytheridae which precludes synonymy with the present genus. Confusingly, in the same paper Kozur (1970a) also established Judahella as a subgenus of Triassinella. The species illustrated by Kristan-Tollmann et al. (1991b, pl. 8, fig. 1) as Triceratina,fortenodosa (Urlichs, 1972) is a species of Judahellu.
Sohn (1 968) discussed the possible relationship between Judahella and Liasssic species of Trachycythere Triebel & Klingler (I 959) which also bear large tuberculae. However, the disposition of tuberculae in the two genera is quite different and we believe that this similarity is merely homeomorphic (see further discussion on Trachycythere below). Judahella andrussovi Kozur & Bolz, 1971 of Kristan-Tollmann et ul., 1991a,b resembles another Liassic genus, Paratrachycythere Park, 1987. That genus was named €or its superficial similarity to the younger Trachycythere (Triebel & Klingler), which is unfortunate because the two Liassic taxa are quite different, particularly in hingement, size and lateral outline. Neither genus can be confidently related to Judahella which we consider to be a valid cytherurid taxon. There is evidence that Judahella ranges back to at least the Late Permian of northern Hungary (Kozur, 1985). In the same publication a new genus was erected, Buekkella Kozur, which may be a junior synonym of Judahella.
Subgenus Judahella (Costuhellu) Kozur, 1971 Type species. Judahella (Costahella) hungaricu Kozur, I971 (p. 28, pl. 2. fig. 6). Remarks. Erected as a subgenus of Judahella Sohn, based on the presence of a rib below the four main dorsal tubercles. In our opinion this is at best a specific character, or common to a group of Judahella species, and the diagnosis of Judahella has been emended above accordingly. We consider the subgenus to be a junior synonym of Judahella.
Genus Kerocythere Kozur & Nicklas, 1970 Relzocythere Kristan-Tollmann: 46 Type species. Cythere raibliana Gumbel, 1869 (p. 184, pl. 6, fig.  36a). Diagnosis. Carapace elongate, triangular in lateral view, greatest height near anterior margin. Dorsal margin straight, ventral margin convex, greatest length above mid-height. Carapace outline triangular in end view with greatest width across ventral surface. Surface of valves smooth or reticulate. Valves bear distinct circum-marginal ribs or flanges (which may be perforate, see Kristan-Tollmann et al., 1991a, pl. 2, figs l,2), cardinal angles well marked and may bear projections. One species, Kerocythere bulbosa (Kristan-Tollmann, 1972), also possess large bulbous inflations anteriorly. Eye spots weak or absent. The hinge is very characteristic. The terminal elements in the LV are single smooth loculi, while the median element, a possibly denticulate bar, is extended distally (both anteriorly and posteriorly) into a large hemispherical boss. Remarks. The genus was originally placed in the Trachyleberididae. In the type description Kozur & Nicklas (1970) designated Cythere raibliana Gumbel, 1869 as the type species but did not figure any new specimens of that species. They figured three species, two of which were referred to Kerocythere n. sp.1 Bolz and Kerocythere n. sp.2 Bolz and the third to Kerocythere n. sp. The reason for reference to Bolz on this publication is unclear.
Kerocythere sp.1 Bolz (Kozur & Nicklas, 1970, pl. 2, fig. 1) possesses three distinct longitudinal ribs (dorsal, mid-and ventral), a denticulate anterior margin and a weak eye spot. Kerocythere sp. 2 Bolz (Kozur & Nicklas, 1970, pl. 2, fig. 2) possesses a dorsal, ventral and antero-marginal rib. The dorsal part of the ventral rib displays a series of short vertical riblets. The antero-cardinal angle terminates in a small boss while the postero-dorsal cardinal angle possesses a short, dorso-ventrally projecting spine (an extension of the dorsal rib). Kozur & Nicklas (1970) also figured material assigned to Kerocythere n. sp. which is probably a juvenile of one of the aforementioned species.
According to Kozur & Nicklas (1970), the genus possesses an amphidont hinge, this is both phylogenetically unlikely and entirely unsubstantiated by the illustrations. Indeed, the hingement appears to be peratodont (sensu Bate, 1972), whereby the median element is inflated terminally. Indeed, from the available illustrations it appears that the terminal teeth (in the right valve and terminal inflations of the median element in the left valve) are very strongly developed, although this may be an artefact of the illustration process (possibly retouched). The hingement is better illustrated in Kozur, 1971 (pls 7 & 8), indeed pl. 7, fig. 5b shows a crenulate median element although this too may have been manually retouched. The hingement closely resembles that of certain Campanian to Recent taxa belonging to the Pectocytheridae, an essentially Southern Hemisphere and mostly Pacific family whose hinge is termed pentadont (Hanai, 1957), which seems to be synonymous with holoperatodont, the former having priority. We consider Kerocythere to be a valid cytherurid genus with a distinctive carapace outline, ornament and hingement.

Remarks. A subgenus which was originally distinguished from
Kerocythere sensu .strict0 by the presence of a median rib, which we consider to be a differentiating character at species level only. Furthermore, the type species is almost certainly a junior synonym of Kerocythere veghae Kozur, 1971(in Bunza & Kozur, 1971. Kristan-Tollmann (1972) made no reference to this species when erecting the subgenus nor did she reference the publication and it is probable that she did not see it before publishing her work. We do not accept the validity of this subgenus and have emended the diagnosis of Kerocyfhere to accommodate it.
Remarks. The genus was originally described from Liassic sediments in the Paris Basin and was placed within the Cytherinae. This medium-sized genus was named for its lophodont hingement which, in Fact, now seems to be merodont with a weakly crenulate median element. Subsequently, Gramann (1962) assigned one new species (Lophodentinu? buchi) and one undescribed Liassic species to this genus. Those latter two species we consider to belong to Eucytheruru. The taxonomic status of Lophodentinu remains in question but may be a valid genus. The earliest representatives of the genus are probably Liassic. Given its large size, carapace shape and lateral outline we do not consider this to be a cytherurid.
The type species described and figured by Bunza & Kozur (Mockella muelleri, p. 8, pl. 1, fig. 12) was originally assigned to the Glorianellidae which is now considered to be a junior synonym of the Limnocytheridae (Whatley & Moguilevsky, 1998). From published illustrations and the original generic diagnosis, we infer that Mockella is a senior synonym of both Dettermunia Sohn, 1987 andHusibuana Kristan-Tollmann (in Kristan-Tollmann &Hasibuan, 1990). Lord et al. (1993) figured a nomina aperta species of Renicytherura Grundel, 198 1 from the Early Jurassic off Western Australia which may be congeneric. We therefore consider Mockella to be a senior synonym of Detterniania and Hasibuana and to be a valid genus of the Cytheruridae, Cytherurinae.
Genus Mostlerella Kozur, 1971 Type species. Mostlerella nodosa nodosa Kozur, 1971 (p. 38, pl. 4, figs 10, 12, 14, 16). Remarks. Kozur assigned two new species to this genus. Both possess a very straight dorsal margin, bulbous swellings along the dorsal margin and a ventro-lateral rib. These features accord well with the emended diagnosis of Judahella (see above). Kozur originally described the genus as possessing a lophodont hinge, however, Kristan-Tollmann (1982) illustrated a number of Mostlerella species and emended the diagnosis to include a noridont hinge. We regard this genus as a junior synonym of Judahella.

Remarks.
Originally erected as a subgenus of Lophodentinu, illustrations of the type species clearly show great similarity with the type species of Rutlandella (Rutlundellu transversiplicata Bate & Coleman, 1975) which is a junior synonym of Eucytherura (see below). All of the species assigned to this genus are congeneric and we regard Movschovitschia as a junior synonym of Eucytherura.
Genus Paratrachycythere Park, 1987 Type species. Paratrachycythere pseudotubulosa Park, 1987 (p. Remarks. This taxon was originally named for its alleged similarity to Trachycythere tubulosa Triebel & Klingler, 1959. The lateral tubercles which are the main feature linking the two genera can also be found, albeit weakly developed, in Eucytherura species from the Liassic of the Danish Embayment (Michelsen, 1975 as Acrocythere). We believe this feature is homeomorphic and that the two genera (Eucytherura and Trachycythere) are distinct and probably unrelated. We consider this genus to be a junior synonym of Eucytherura.
The suprageneric position of genera such as Trachyc-ythere remains in question. It was originally assigned to the Trachyleberididae, however, that family 1s now considered to range from the Early Cretaceous.

323,
Diagnosis. Carapace small, rounded, ovate elongate outline in lateral view. Dorsal and ventral margins weakly convex. Ornament variable but usually dominated by longitudinal ribs with secondary reticulation. Lateral projections rare. Hinge lophodont. Vestibulate. Remarks. This valid cytherurid genus, which extends from the latest Triassic through to the Cretaceous and possibly into the Early Cenozoic, lacks the distinct eye tubercle and posteroventral projection of Eucytherura. It can also be distinguished by its more elongate, lanceolate carapace lateral outline. It differs from Cyzherura Sars in the presence of vestibula. Ornament is dominantly of ribbing rather than reticulation, although some species are smooth or very weakly ornamented. Recent examination of Anderson's (1964) Rhaetian material has revealed that Metucytheropteron nannodes Anderson belongs pl. 6, figs 1-8) .
to Procytherura, thus extending the range of this genus back to the Late Triassic.
Genus Rutlandella Bate & Coleman, 1975 Type species. Rutlandella traizsversiplicata Bate & Coleman, 1975 (p. 34, pls 13.7-13.10, 13.12, text figs 14a,b, 15, 16). Remarks. This genus was erected on characteristics which are essentially specific. Within the literature there are a number of closely related species which have been assigned to genera such as Rutlandella, Movschovitschia and Eocythereis. We do not consider that these species warrant separate generic status and, therefore, Rutlandella is placed in synonymy with Eucytherura.
Genus Simeonella Sohn, 1968 Type species. Simeonella brotzenorum Sohn, 1968 (p. 23, pl. 2, Remarks. Simeonella Sohn, 1968 was described from the Triassic of Israel. The carapace is sub-rectangular in lateral view, inflated laterally with a reticulate external surface and an antimerodont hinge. Sohn (1968) placed it questionably in the Cytheruridae, while Bunza & Kozur (1971) placed it in the Progonocytheridae. Sohn suggested that Scabriculocypris Anderson, 1940 andTchunguania Zhong, 1964 may be synonymous with Simeonella. Tchunguania, however, is a non-marine genus belonging to the Permianidae, which is characterized by the possession of 3 adductor muscle scars (Whatley & Moguilevsky, 1998). Sohn also placed some Chinese species of Gomphocythere described by Zhong (1964) into Simeonella. We disagree with Sohn on these possible synonymies. We follow Whatley & Moguilevsky (1 998) who placed Simeonella in the Cytherissinellidae in possible synonymy with Lutkevichinella Schneider (in Mandelstam et al., 1956). They also subsumed the Cytherissinellidae within the Limnocytheridae, Limnocytherinae. The adductor muscle scar pattern clearly precludes the inclusion of this genus within the Cytheracea and therefore the Cytheruridae.
Genus Sohnetta Kozur, 1971 Subgenus Sohnetta (Sohnetta) Kozur, 1971 Type species. Sohnetta (Sohnetta) meulleri Kozur, 1971 (p. 42, pl. 2, fig. 8). Remarks. From the type figure and description, the genus possesses a very small, sub-triangular carapace and the hinge is probably lophodont. In our opinion this taxon certainly belongs to the Cytherurinae (Cytherurinae). Only one figure was given of the holotype which is sub-triangular in lateral outline, has a slightly convex dorsal margin and two dominant longitudinal ribs extending from postero-dorsal to antero-ventral. The type species is easily accommodated within Eucytherura. Kristan-Tollmann (1983, p. 153) placed the type species into Judahella (Costahella), however, the lack of tubercles and convex dorsal margin distinguish this species from Judahella. We consider Sohnetta to be a junior synonym of Eucytherura.
Genus Boogaardella Kozur, 1971 Type species. Sohnetta (Boogaardella) triassica Kozur & Bolz nsp. in Kozur, 1971 (p. 45, pl. 5 , figs I , 3-5). Diagnosis. Carapace small, triangular to sub-rectangular in lateral view, dorsum and venter straight and convergent posteriorly, anterior and posterior margins broadly rounded. Carapace only weakly inflated, trapezoidal in dorsal view, broadest in posterior %. Lateral surfaces reticulate and bear strong ribs and minor tubercles. Strong ventro-lateral rib extends along anterior margin. Smaller transverse ribs originate at postero-dorsal tubercle. Internal features unknown. Remarks. The subgenus Sohnetta (Boogaardella) Kozur was erected in the same publication as Sohnetta (Sohrrrtta). However, the poor quality of the illustrations precludes a complete review of the relationship between these taxa. In our opinion the type species, Sohnetta (Boogardella) triassica Kozur, is clearly a cytherurid characterized by its small carapace size and ornamentation. Although external ornament is similar to that of other taxa discussed herein we have retained this as a valid genus due to the distinctly different carapace shape which is much more angular in lateral view that that of Judakellu. More importantly the outline in dorsal/ventral view (Kozur, 1971, pl. 5 , fig.lc) is distinctly unlike that of any other contemporaneous species.
We conclude that Sohnctta (Boogar-de//a) is a valid genus while Sohrzettu (Solinetta) is a junior synonym of Eucytherura. Boogardella is therefore raised to generic status.
Genus Speluncella Schneider (in Mandelstam et a/., 1956) Type species Speluncella spinosu Schneider (in Mandelstam et al., 1956, p. 120, pl. 19, fig. 3). Diagnosis. Egg-shaped, very rounded anteriorly, almost pointed posteriorly, smooth apart from ventro-lateral and ventral ribs (after Whatley & Moguilevsky, 1998). Remarks. Whatley & Moguilevsky (1998) retained this genus in the family Spelluncellidae which they subsumed within the Limnocytheridae, Timiriasevinae. Bunza & Kozur (1971) tentatively assigned a new species (Speluncella? kurnica) to this genus but provided only two unremarkable line drawings to illustrate it (pI.1, fig. 2a,b). These drawings are similar to some species of Cytheropterinae. However, without examination of the type material or clearer illustrations it is not possible to confirm Its taxonomic position. We consider the genus to be a valid taxon but not a cytherurid. Spr/unc& may be a senior synonym of Bloniella.
Genus Telocythere Kozur, 1970bKozur, . 1973 Veghicythere Kozur: 14. Type species. Glorianella?jischeri Kozur, 1968a (p. 860, pl. 2, fig.  12ax). Remarks. The type species is elongate sub-rectangular in lateral view, laterally compressed with longitudinal ribs. It was described from brackish-water deposits in association with Darcvinula and Chara. The genus includes a number of species assigned by Kozur (19704 to Lutkevichinella (Cytherissinellu) which Whatley & Moguilevsky (1998) included within the Limnocytheridae. Although the type species is somewhat similar in its external morphology to some Liassic cytherurids, there is no strong evidence to support its placement in the Cytheruridae. Based on the limited illustrations and descriptions available it is difficult to reconcile the inclusion of species such as T. tollmanni Kozur (1970b) in the same genus as the type species and there are major inconsistencies jn that particular study. Pajunites, also described by Kozur (1970b), may be congeneric with T&cyfhere. Whatley & Moguilevsky (1998) suggested that Pajanites may belong within the Limnocytheridae, Timiriaseviinae, the brackish-water ecology of the type species supports the inclusion Telocythere within the Limnocytheridae. Telocytlzere may be a valid genus but is not a cytherurid.
Genus Trummerrlla Kozur, 1973 Type species. Timiriasevia qfentalensis Urlichs, 1972 (p. 686, pl. Remarks. Although the familial assignment of this genus is uncertain, it is clearly not a cytherurid. The poor quality of the type illustrations render it impossible to establish its true familial status. The ornament resembles that of Tinziriasevia, a Triassic to Early Cenozoic, fresh-brackish-water genus, but the carapace shape is distinctly different. Indeed, the carapace shape is similar to the exclusively Triassic, brackish-water genus Rhombocythere (Anderson, 1964) Kozur, 1971 (p. 47, pl. 2, fig. Remarks. The carapace is triangular in lateral outline with noding along the dorsal margin. There may be a lateral spine, but the type figure is unclear. There is at least one strong anteriorly produced spine (others may be missing). According to Kozur (pers. comm.), this is a marine deep water taxon. It has similarities to some deep-sea species of Eucytherura (such as Eucytherura parabatularia Ayress rt a/., 1995) from the Cenozoic of the Pacific, if a little larger. Many aspects of this species suggest that it may well belong to the Bythocytheridae (straight dorsal margin, lateral spine and nodes), possibly related to genera such as Nagyella (Kozur, 1970a). This can only be resolved through studies of the adductor muscle scars; until then it is not possible to determine the validity or the familial status of this genus.

7).
Genus Veghicythere Kozur, 1973 Type species. Lutkevichinella (Cytherissinellu) multistriata Kozur, 1970a (p. 402, pl. 2, figs 6-7). Remarks. Externally the type species is very similar to Telocythere jscheri, the type species of that genus, which we consider to belong within the Limnocytheridae. The external ornament of longitudinal ribs is also similar to that of some Liassic species of Procytherura but we d o not believe this to be taxonomically significant. The genus is probably a junior synonym of Telocythere and, therefore, not a cytherurid.

SUMMARY
A summary of our taxonomic review is given in Table 1 and the stratigraphical distribution of valid genera is presented in Fig. 1. It is well documented that many faunal and floral lineages did not survive the mass extinction at the close of the Permian and the Ostracoda are no exception (Whatley et nl., 1993). Many of the major post-Palaeozoic ostracod families were established by the mid-to Late Jurassic and we are now in a position to outline the rise of one family in particular, the Cytheruridae.
1. It is clear that certain members of this family already existed during the Permian (namely Judahella and Gruendelicythere, recorded by Kozur (1985) from northern Hungary). 2. The great similarity between some early Cytheruridae (Triassic-Early Jurassic) and Early Mesozoic Bythocytheridae (which are distinguished by the possession of five rather than four adductor muscle scars) suggests that certain elements of this polyphyletic family may have arisen from the Bythocytheridae. Indeed, this may also have been the origin of genera such as Judahella during the Late Palaeozoic. The Bythocytheridae are the oldest and longest-ranging Podocopida (Ordovician to Recent). 3. External characteristics and gross carapace morphology also support the suggestion of Grundel & Kozur (1975) that some post-Palaeozoic Cytheracea may also have derived from the Palaeocopid Kirkbyacea (Devonian-Triassic). 4. Finally, it is significant to note that many of the Triassic assemblages referred to above are recorded from shallow shelf and marginal marine (even brackish-water) environments. The opening up of new environments consequent upon the global rise of Triassic sea-level clearly played an important role in increasing marine biodiversity at this time.
There are a number of papers describing Permian ostracod assemblages which may provide evidence of links between Palaeozoic and post-Palaeozoic ostracod lineages (Kozur, 1981(Kozur, , 1985(Kozur, , 1991a(Kozur, , 1991bGerry et ul., 1987;Kniipfer, 1967). Gerry et al. (1987) included a new genus, Arqoviellu, which may be ancestral to Triassic-Early Jurassic genera such as Ektyphocythere Bate, 1963. Although this review deals essentially with the Cytheruridae, other podocopid lineages which first appeared in the Early Mesozoic also had their origins in Late Permian and Triassic times. A particular problem surrounds a number of genera recorded from Liassic sediments in NW Europe (e.g. Kinkeli- nella, Ektyphocythere, Pleurifera) which may have evolved from, or even belong to, the Cytheruridae given their merodont hingement, simple marginal pore canals and muscle scar patterns. While a study of these taxa is beyond the scope of this review, it is important to realize that such taxa may also be ancestral to other families which, with evolution, become readily separable during the Middle Jurassic. Such famiiies include the Cytherideidae, Schulerideidae, Progonocytheridae and Protocytheridae.
The physical and biological pressures which acted upon Early Mesozoic faunas to bring about relatively rapid diversification were not confined to the early Cytheruridae; they also caused other families to become abundant and diverse.