Maastrichtian Heterohelicidae (Planktonic Foraminifera) from the North West Atlantic

Relative frequencies of heterohelicid species in the Maastrichtian of DSDP Site 605, DSDP Hole 111A and Imperial Oil/Amoco core hole C23 on the Grand Banks have been estimated to show temporal and geographic variation patterns in terms of Cretaceous faunal provinces. Heterohelix globulosa and H. planata dominate the shallow marine heterohelicid faunas of core hole C23. Together with H. dentata and H. glabrans they are the most common forms in the temperate faunas from Hole 111A. Pseudoguembelina spp are common in the Tethyan faunas from Site 605 but are rare in Hole 111A. Racemiguembelina spp and fully developed Pseudotextularia spp exclusively occur at Site 605. A distinct but unexplained faunal boundary within the Site 605 section involves frequency shifts of three “relatively cold” species. H. dentata, H. glabrans and H. planata. Dissolution effects, expressed in changes in the relative frequencies of H. globulosa and Pseudotextularia elegans, are present in several intervals across the section. H. globulosa is the most sensitive for dissolution. Pst. elegans is resistant, as are to a lesser extent, Gublerina cuvillieri, Pseudoguembelina excolata, Psg. palpebra, and Planoglobulina acervulinoides.


INTRODUCTION
This stud:y concerns the Upper Cretaceous planktonic foraminiferal family Heterohelicidae Cushman in Maastrichtian and some Upper Campanian sediments from the NW Atlantic. Many heterohelicid species show biostratigraphic potential, especially, but not only, the multiserial forms. Yet, relatively little attention has been paid to the heterohelicids, and their biostratigraphic and biogeographic distribution are not know in much detail. In this study, heterohelicid faunas from three NW Atlantic localities (Fig. 1 ), representing different faunal provinces, are compared. The upper Lower Maastrichtian and Upper Maastrichtian of DSDP Hole I 1 1 A represent a temperate environment (Nyong, 1984); the Upper Maastrichtian at DSDP Site 605 has a tropical fauna, with coldelements (Jansen and Kroon, 1987). The Upper Campanian/Lower Maastrichtian section of Imperial Oil,lAmoco core hole C23 on the Grand Banks, South of Nova Scotia, represents shallow water deposits. Since there is little agreement on heterohelicid taxonomy, this study discusses the heterohelicid species concept in some detail.
The heterohelicids from DSDP Site 1 I 1 have been previously studied by Martin (1972) and Weiss (1983). Jansen and Kroon ( 1987) included heterohelicids in their study of the planktonic foraminifera of the Maastrichtian in DSDP Site 605. Nyong (1984) included Site I 1 1 in his analysis of North Atlantic faunal provinces. However, these studies give qualitative or, at best, semi-quantitative results. While the results presented below agree with their general conclusions, the quantitative approach used here allows for a more detailed analysis of faunal changes. Heterohelicid species distributions were calculated from counts of some 300 specimens from the > 125 pm size fraction of each sample. The percentage of benthic foraminifera was determined for each sample, to give an indication of the depth of deposition, and (or) dissolution effects. The percentage of heterohelicids within the planktonic association, and that of globotruncanids within the spirally coiled plankton give additional environmental information.
Planktonic and benthic foraminifera were qualitatively searched for biostratigraphic markers. The planktonic fo- raminiferal biozonation follows that of Caron (1 985). The 63-125pm size fraction was scanned for the presence of additional small sized Heterohelicid species. The material is filed in the micropalaeontological collection of the Geomarine Center of the Free University in Amsterdam.

Grand Banks
Grand Banks core hole C23 is one of a set of 25 holes drilled by Imperial Oil/Amoco in 1965. Sediment-ages between holes range from Paleozoic to Cenozoic. Hole C23 is the only one from which Upper Senonian sediments have been recovered; a 95m thick section of black to grey bioturbated clays is unconformably overlain by 250m of Eocene and younger sediments. Twelve samples from four 3m long cores, taken at approximately 25m intervals, were available for this study ( Figure 2). They contain excellently preserved foraminifera1 faunas that are rich in benthos (around 70%, Fig. 2), accompanied by low diversity plankton. At the present day, such a high percentage of benthic foraminifera is found on the middle shelf areas (Wright, 1977, Van Marle andothers, 1987); the same shallow depth of deposition seems a probable estimate for the core hole C23 deposits.
Planktonic age-marker are absent. The presence of the benthic species Neoji'ahellina praereticulata Hiltermann and Bolivinoides draco miliaris Hiltermann and Koch give an upper Campanian to lower Maastrichtian age ( Van Hinte, 1967, 1976Koch, 1977). Because the C23 section is older than the other sections studied here, only the presence of any morphotype in common with the other localities can be used to give information about heterohelicids in shallow water deposits. The absence of any species may not only be due to the shallow depth of deposition, but also to differences in age.

DSDP Hole l l l A
The Maastrichtian foram-nanno chalk ooze of DSDP Hole 1 1 I A core 1 1 was deposited at an outer sublittoral to upper bathyal depth ( van Hinte, 1972). The presence of Glohotruncana gansseri Bolli in the lower samples ( 1 1 cc to 11-2, 73-76 cm) gives an G. gansseri Zone age, the zonal marker Ahathomphalus mayaroensis (Bolli) is present in the upper four samples, 11-2, 2-5cm to 11-1, 137-140cm. The section is unconformably overlain by lower Eocene sediments, The upperpart of the A . mayaroensisZone is missing. The 20 samples from the 8m thick section contain between 5 and 15% benthic foraminifera, with a peak of 30% in sample 1 1 1A-11-6, 143-147cm in the lower part of the section (Fig. 3). While the relative frequencies of the heterohelicids do not change much between samples, the number of globotruncanids relative to other coiled planktonics is more variable. The globotruncanid frequencies are high i n the upper and lower samples; they are lowest in the middle part of the section, around 18%.
The planktonic foraminifera show signs of dissolution (dissolution holes, fragmentation) and it is possible that the shifts in the relative benthos-and globotruncanid-frequencies are the results of preferential dissolution, although not necessarily because of a rising CCD. The samples were washed onboard, during Leg 12, using a strong solvent, that may corrode samples, if they are left standing too long. The effects would be indistinguishable from primary dissolution in the lysocline.
As in the Grand Banks samples, H. glohulosu und H . plunutu form the bulk of the heterohelicid faunas, but at this Site they are accompanied by more species. Representatives of all Maastrichtian genera, except Rucemiguemhelinu, are present, although mostly in low numbers. Pessagno and Longoria ( 1972) reported the presence of Rucemiguemhelinu powelli (=Rucemiguemhelinu sp) in the A . muyaroensis zone of Hole 1 1 IA, but this species was not encountered during this study.
Apart from H.glohulosu and H. plunutu, H . dentutu and H . gluhruns are the most common species throughout the section. The higher relative frequencies of Plunoglohulinu ucerwlinoides (Egger) in the upper samples, 1 1 -1, 137-140cm to 1 1-2,2-5cm and of Plunoglohulinu riogrundensis (Martin) in sample 1 Icc coincide with higher relative frequencies of globotruncanids, and may be due to differential dissolution. The first occurrences of PI. ucervulinoides, Planoglohulina multicumerutu (de Klasz) and of Pseudotextuluriu intermedia de Klasz in the G. gunsseri Zone are in agreement with the ranges given for those species by Martin (1972), Masters ( 1977 and Weiss (1 983).
The overall faunal composition in Hole 1 1 1A described here differs considerably from the results given by Weiss (1983). who studied a larger size fraction (>200pm) than here (> 12Spm). On a presence/absence basis, the differences between the two datasets are mainly taxonomic artfacts. However, in his >200pm size fraction, the heterohelicids as agroup are arare part of the planktonic foraminifera1 faunas, while here, in the > 12Spm size fraction, they constitute around 25%. Heterohelix spp. that form the bulk of the heterohelicid faunas are generally small-sized, and would only rarely be present in larger size fractions.

DSDP Site 605
At Site 605 DSDP drilled a SSm thick section in upper Maastrichtian grey foram-nanno oozes and marly oozes. Backtracking gives a bathyal depth of deposition of about 2.Skm (Jansen and Kroon, 1987). The planktonic foraminifera give an upper G. gunsseri Zone (samples 71cc to 69-5, 60-62cm) and A . muyuroensis Zone age (samples 69-4, 60-62cm to 66-2,28-30cm), based on the presence of the respec-rive zonal markers. The A . niuyuroensis Zone is complete in Site 605 as the K/T boundary is found in the interval around 66-I , 75cm (Smit and Van Kempen, 1987) The 39 samples studied contain diverse planktonic foraminiferal faunas, with generally low numbers of benthic foraminifera (between 0-5% of the total foraminiferal faunas; Fig. 4). Three samples, 605-66-2,28-30cm, 66-2,59-61cm and 66-3, 59-61cm, clearly contain a higher amount of benthic foraminifera; the heterohelicid and globotruncanid frequencies are also higher than in other samples. These are though to represent carbonate dissolution due to a rising CCD: the samples contain a much lower number of foraminiferal specimens than the others, and the relative frequencies of many species fluctuate drastically in this interval (Figs. 4 and 5 ) . The frequencies of groups of foraminifera with heavy tests especially show a relative increase.
DSDP Site 605 has the most diverse heterohelicid fauna of the 3 sample sets. Yet, H.glohu1osu is the dominant form with relative frequencies that are approximately the same as in Hole I 1 1 A and the Grand Banks samples. H. planutu gave way to higher frequencies of other species (Fig. 5 ) ; H . plunutu is usually rare in the Site605 samples. Pseudoguemhelinu spp and Psrudotestuluriu spp are more common than in the two northern localities. Pseudotextuluria specimens with a fully developed, deep test are present. Additionally, Pseurloguemhelinu sp and Rucwniguemhrlinu spp were found in Site 605, though generally in low numbers. The ranges of Ruc~cmi~gurmheIinujru~~tic~~~.~u (Egger) and of Ruceniiguem-hc~linupowrlli Smith and Pessagno coincide with that of the zonal marker A. muyuroensis.
Within the Site 605 sample set two faunal trends can be distinguished. The first is mostly expressed by the frequencies of H . plunutu, H . dentutu and H . gluhruns. H . gluhruns and H . plunutu are consistently present to common, in the lower samples (7 Icc to 68-4,60-62cm), but become rare in the upper samples (68-3, 60-62 to 66-2, 28-30cm). H . dentutu shows an opposite trend; it is mainly confined to the upper samples. A second faunal trend is shown by changes in the relative frequencies of H. glohulosu and, for the upper samples, Psrudotextulariu r1egun.s (Rzehak).
The two phenomena are apparently unrelated. The H . ,qlohulosa and Pst.eleguns frequencies are constant across the interval in which H.planuta, H . dentutu and H . gluhrtins show their reversal. The independence also shows in the correlations between the frequency distributions of the vari- ous species found at Site 605 ( Fig. 7). H. glohulnsu frequencies have no clearly positive correlation with any of the other species. Pst. rleguns is part of a group of species that also includes PI. ucenwlinoidrs. Pseurio~gueniheliriu r.u.olutu (Cushman), Psrudoguemhelinu pulprht-u Bronnimann and Brown and Psrudoguemhelinu sp. This group shows the opposite of the H . glohulnsu trend, with which species it is negatively correlated. In the same manner H. g/Uhrm.Y and H . plunatu are negatively correlated with H . dentutu, and to a lesser extent with Plunoglohulina c~urseyie (Plummer). Yet, the last four species are mostly uncorrelated to either H . glohirlosu and Pst. elr,qun.s frequencies (Fig. 6.) Malmgren ( 1987) showed that ofthe Maastrichtian planktonic foraminiferal species, H . glohirlosu is the most susceptible to dissolution. Indeed, the lowest frequencies of H . ~qlohulosu (below 20%) and the highest of Pst. eleguns (over 30%1) are found in those samples that contain a high percentage of benthic foraminifera, and show effects of partial  dissolution. samples 66-2,28-30cm, 66-2,59-6lcm and 66-3,59-61cm (Figs. 4.5). The second faunal trend in the Site 605 samples is therefore considered to be the result of differential effects of increased dissolution, due to a rising CCD.

DISCUSSION AND CONCLUSIONS
The strongest dissolution is found in the uppermost part of the Site 605 section. There the relative proportion of benthic foraminifera increases as well. That the benthic foraminif-era1 content remains low in the other dissolution affected samples ( Fig. 6) can be explained by assuming that dissolution effects are not strong enough to influence the P/B ratio much. Studies of Recent material show that indeed the faunal composition changes due to dissolution effects before a clear change in the PlanktonBenthos ratio can be noted (Troelstra, 1984).
It appears that Pst. eleguns and, to a lesser extent, P s g . ccr-cvltura, Psg . pulpehr-u G. CYI villieri7 Pseudoguemhelinu sp and PI. ucwvulinoides are dissolution resistant forms, Malmgren ( 1987) found that only Psg. palpehra is dissolution resistant, while Pst. elegans and PI. aceriwlinoides (=Planoglohulina hrazoensis Martin in Malmgren's synonymy) showed no changes in frequency with increasing dissolution effects. The difference may be partly due to the fact that he did include the globotruncanids in his counts, while here the frequencies are measured relative to other heterohelicid forms only. The globotruncanids, with their heavy tests, would be dissolution resistant, and their relative increase might dampen the effects on the frequency changes of other, slightly less dissolution resistant forms. On the other hand, a differential initial faunal composition will cause different dissolution related frequency changes, since frequencies can only be measured relative to other species.
By analogy, it is likely that the changes in the Hole 1 1 I A heterohelicid faunas are also related to dissolution effects,     Fig. 7 Heterohelix navur-r-oensis without an initial spiral coil. Sample C23 75-12, aedge view, bside view. Fig. 8  Discounting dissolution related changes, a comparison between the three localities of relative frequencies in dissolution free samples does show biogeographic trends, as do the presence-absence patterns of heavy tested forms in dissolution affected samples. The Grand Banks samples represent a shallow marine environment. DSDP Hole l l l A represents temperate waters (Nyong, 1984), and the Site 605 faunas are tropical, with cold elements (Jansen and Kroon, 1987 H . glahranscan be added to this list. Together, the four forms dominate the transitional faunas of Hole 1 I I A (discounting the frequencies of PI. acervulinoides, which is here considered to be dissolution related). H. glohulosa and H.planata are also dominant in the shallow deposits from the Grand Banks, where H. glahrans and H . dentata are very rare. This may signify that the first two species were more tolerant of variable shelf conditions than the latter two, but it can also be explained by a difference in depth habitat. Boersma and Shackleton ( 198 1) concluded that striate Heterohelix spp (including H. glohulosa and H.planata) were surface dwellers, while the smooth heterohelicids (including H . dentata and H . gluhrans ) lived deeper in the water column.
Other species show opposite geographic trends. The Pseudoguernhelina spp are more common (or less rare) at Site 605 than at Site 1 1 I , concurring with their mostly tropical occurrences observed by Sliter (1 976). Racemiguernhelina spp. are confined to Site 605. The biserial pseudotextularian forms appear to be mostly tropical as well. Pst. elegans is found at Site 605 only, while Pst. nuttalli is present at Site 11 1, but only forms with a narrow test.
More than the other three "cold"forms, H . planata seems to be at home in the northern waters. This species shows a distinct decrease in the more southern Site 605, where the relative frequencies ofH. dentata, H . glahi-ans and H . glohulosa are in the same order of magnitude as at Site 1 1 1. While the higher diversity at Site 605 indicates a tropical environment, the presence of those "cold" water forms makes it difficult to relate the faunal change at Site 605 to specific oceanic processes. Abundant radiolaria in the Paleocene at Site 605 indicate cold, nutrient rich waters (Nederbragt and Van Hinte, 1987), either surface waters from the Labrador Sea, or upwelling. Possibly, the same water circulation patterns already influenced the Maastrichtian faunas; it would explain the combination of cold and warm species. The decrease of H . planata might then be interpreted as a change in the upwelling regime, or as a warming event. Unfortunately, these hypotheses cannot be tested by stable isotope analysis. Most specimens are calcite filled, and the preservation of the faunas is too poor to give reliable results.
Representatives of the multiserial genera Planoglohulina and Guhlerina show approximately the same frequencies at both DSDP Sites. This indicates a relatively widespread geographic distribution. Since these rnultiserial forms have relatively short age ranges, it increases their value as biostratigraphic markers.

SYSTEMATIC NOTES
A short discussion is given, when appropriate, of important morphologic features of the heterohelicid species encountered during this study. Some less well known species are described in more detail. The descriptive terminology for the heterohelicid tests is shown in figure 8. The patterns of multiserial growth that can be encountered in the heterohelicid generaaredescribed in detail in Nederbragt, 1989. Only the most important synonymies are discussed.   DSDP 11 1A-11-2, top, aedge view; bside view.

Remarks.
Here, the emendation of G. cuvillieri as given by de Klasz (1953b) is followed. In the material studied here multiserial growth is absent, only biserial specimens have been found. Distribution. Very rare in Hole I 1 1A. At Site 605 confined to the upper part of the section.
Genus Heter-ohelix Ehrenberg, 1843 Type species: Spiroplectu urncv-icuna Ehrenberg, 1844. Heterohelix dentata Stenestad, 1968 (PI. I , figs. 4-7) 1968 Heterohrlix dentutu Stenestad: 67,68,pl. I ,8,9; pl. 2, figs. 1-3. Description. Test biserial, or with an initial spiral coil, wall microperforate, smooth. Periphery acute to subacute, chambers elongate in side view, straight to reinform. Aperture bordered by distinct flanges. Remarks. The morphotype described above has variously been recorded as H . gluhruns (Sliter, 1976;Weiss, 1983) or as H . pulchra (Masters, 1977;Jansen and Kroon, 1987). It differs from H . glahruns in its more reniform chambers, and from H . pulchru in its more acute periphery and smaller apertural flanges. These differences appear to be consistent, and sufficient to distinguish H . dentata as a separate species. Its occurrence in our Maastrichtian samples agrees with the range given by Stenestad (1969). Smith and Pessagno (1973) described the presence of "accessory apertures" in Heterohelix glahruns (Cushman). The same structures were encountered both in H. gluhruns and in H . dentata (PI. I , fig. 7). However, they are not true apertures, but relict exposures of the apertural flaps of preceding chambers. Distribution. Rare in core hole C23, rare in the lower part but common in the upper part of the Maastrichtian of Site 605. A common species in Hole 1 1 1 A, and therefore thought to be tolerant to colder waters. tleterohelix glahrans (Cushman, 1938) (  Fig. 2 Heterohelix sp, with reniform chambers. Sample DSDP 605-69-5, 60-62cm; aedge view; bside view. Fig. 3 Heterohelix sp. Sample 66-3, 28-30cm; aedge view; bside view.   Van Hinte,196.5) a set of chambers is formed at each growth step, resulting in multiserial growth (harmonic growth of Van Hinte, 1965). The chambers of each set enclose all apertures of the preceding set; each set has a relapsed mono-apertured chamber, at alternating sides of the test. Two chambers may merge to form a tri-apertured one. The chambers of each set are numbered, counting from the progressive chamber.
Cside-view of a multiserial Guhlerina test. The pattern of multiserial growth is similar to B, except that the bi-apertured chambers are widely spaced and connected by extended apertural flanges (indicated by thin lines); the progressive chamber is shaded.
D -2) side-view of a Racemiguemhelina test, in which the multiserial chambers have been traced assuming harmonic growth as in B; the progressive chamber is shaded; 1 )top view of an ellipsoid specimen. For each single chamber in a flat multiserial form, a pair of chamberlets is formed connected by a bridge. The peripheral relapsed chamber remains single; 3) top view of acone shaped specimen, in which all chambers of each set, including the relapsed chambers, are connected by one large structure (a sieve plate, Pessagno and Brown, 1969).
note small, but distinct apertural flanges.
Remarks. Hrterohelix glohulosa specimens may have an initial coil (PI. 2, fig. S ) , or a bi-apertured terminal chamber. Hetrrohelix striata should differ from H . glohulosa in having stronger costae; our material shows transitions from specimens with h e a t e d pustules to lightly constate (PI. 2, fig. 4) to specimens with more heavy continuous costae (PI. 2, fig. 3). The differences are gradual, and interpreted to represent intraspecific variation.

Distribution.
H. glohulosa is the most abundant heterohelicid species in all three localities studied here.
Heterohelix navarroensis Loeblich,195 1 (PI. 2, figs. 6, 7) I95 I Heterohelix navarroensis Loeblich: 107, 108, PI. 12, figs 1-3; text fig. 2. Remarks. H. navarroensis is a small species, that is mostly confined to the 63-125pm size fraction. The larger specimens, found in the > I 25pm size fraction, resemble H . navarroensis in general morphology, but lack the spiral coil (Plate 2, fig. 7). Such forms differ from H . planata in having a less rapidly flaring test. H . navarroensis, with or without initial coil, differs from H. glohulosa in having more elongated chambers and larger apertural flanges. Distribution. Rare in the> 125prn size fraction of the samples from core hole C23 and Hole 605; not observed in Hole 1 I I A .

Remarks.
The specimens here encountered have a smooth test, like the topotypes figured by Weiss (1983). Masters (1977) described H. pulchra as possessing poremounds, and Petters (1 977) also figured a specimen with poremounds. Morphologically, the two types are identical, and are here considered to belong to the same species. The same difference in wall structure among specimens belonging to one species can be found in the Miocene planktonic foraminifer Cassigerinella chipolensis (Cushman and Ponton) (Saito and Biscaye, 1977). Distribution. H . pulchra was encountered in core hole C23 sample 75-1 8 only.
Heterohelix punctulata (Cushman, 1938 Remarks. H. punctulata is often included in Pseudoguemhelina, because of its accessory apertures. It is here included in Heterohelix, since its accessory apertures are not generally present, and, when present, lack the distinct lip that is characteristic of Pseudoguernhelina. The multiserial forms here included in H. punctulata were described as Pst. echevarriai by Seiglie. Such forms resemble the biserial H . punctulata in general morphology; they are here regarded as gerontic individuals, comparable to the multiserial forms found in H. glohulosa and Pseudoguemhelina palpehra (Nederbragt, 1989). Distribution. Throughout Hole 1 1 1A and Site 605, mostly rare. Multiserial forms were found in Hole I 1 I A only.

Remarks.
A variety of forms are here included in Heterohrlix sp, that differ from other species in having relict apertural flanges visible along the median suture, and reinform, costate chambers. A biapertured terminal chamber may be present. Distribution. Rare to common at Site 60.5.  view.

Explanation of
Genus Planoglohulina Cushman, 1927Type Species Guemhelina acervulinoides Egger, 1899 Remarks. Here the interpretation of Planoglohulina given by Martin (1972) and Smith (1978) is followed. Planoglohulinu rnulticameratu (de Klasz) and Planogl(hdina riogrundensis (Martin) are variously included in the genus Ventilahrella Cushman (Martin, 1972, Smith and Pessagno, 1973), or in Planoglohulina (Weiss, 1983. The type species of Ventiluhrvlla, Ventilahrella eggeri Cushman, however, is a late Santonian to early Campanian species, that is phylogenetically unrelated to the Maastrichtian forms here under discussion: no multiserial heterohelicids are found in the upper Campanian (Weiss, 1983). While the phylogenetic relation of PI. multicarnerata and PI. riograndensis with the genotype PI. acervulinoides is unclear, it is here considered preferable to include those two in the genus Plunoglohulina.  Martin: 82,83,pl. 3,fig. 7; pl. 4, fig. 1-2 Remarks. Martin ( 1972) assigned a neotype lo PI. ucwvulinoides, thereby stabilising the species concept. PI. hrazoensis shoulddiffer from PI. acervulinoides in having more inflated chambers, narrower costae and less multiserial chamber sets. However, the holotype of PI. hrazoensis and the neotype of PI. ucervulinoides, appear to be end members of a continuous morphologic series. Most specimens show a combination of the characteristics of the two morphotypes. Therefore, PI. hrazoensis is here regarded as a junior synonym. Distribution and Range. Rare to common in the Maastrichtian of the upper part of Hole 1 1 1 A and throughout Hole 605. It ranges from the middle part of the G. gunsseri Zone to top of the A . rnayaroensis Zone.
I976 P.srudo,guc~mh~~litiu polyidcuru Masters: 3 19, pl. I , fig. 9. Remarks. Psg. cwnutu should differ from Psg. p u l p d m in having a comute-shaped last chamber. Psg. pulphro can also have a subquadrate terminal chamber, or a bi-apertured one. Psg. p o l y p l c w a has been described as having thinner costae. These differences are here regarded as intraspecific 1-7; Distribution. Rare in DSDP Hole 1 I 1 A; more common in Hole 60.5.

Description.
Test biserial, bi-concave in edge-view. An initial planispiral coil is sometimes present. Chambers much deeper than wide. Surface finely costate; aperture a wide, low arc. Remarks. Since the name Pst. elegans is here reserved for the coarsely costate form, another name must be found for the above described morphotype. Guemhelina nuttalli Voorwijk is the next oldest available name. Voorwijk's material is stored in the micropalaeontological collection of the Rijksuniversiteit Utrecht, the Netherlands. Here, the specimen he depicted in figure 4 (Voorwijk, 1937) is designated as a lectotype. The nine specimens he figured are all in one slide (D12267), together with another 21 specimens, of which unpublished drawings were made. All specimens, except one, are finely costate, and are bi-concave in edge view. The main variation is in the shape of the two ultimate chambers, ranging from subglobular to elongate, subrectangular in edge view. Half of his figured specimens can be reliably identified, among them the specimen of figure 4, that is here redrawn ( fig. 9) Fig. 9. Redrawing of A) side view and B) edge view of specimen, corresponding to figure 4 of Voorwijk, 1937, herein designated as lectotype for Guemhlina nuttalli; scale bar = 1 00pm The figured specimens, including the lectotype, may come from Voorwijk's locality 80, as marked on the slide. However, both the original type description and the collection register mention that the drawn specimens are from various localities. Additional slides, with other locality numbers, are present. However, it is here considered preferable to choose a figured specimen as lectotype, even though its locality could be uncertain.
Guemhelina nuttalli was published in February 1937; Guemhelina plummerae Loetterle, a comparable form, was published later in the same year. The difference in strength of costae, described for Pseudotextularia cushmani Brown, is here considered insufficient to distinguish a separate species. Master published Pseudotextularia hrowni as a new name for G. plummerae, that in his synonymy is a subjective secondary homonym of Ventilahrella plummerae Sandidge 1932 (=Pseudotextularia carseyae according to Masters). Distribution. Racemiguemhelina powelli Smith and Pessagno, 1973 (PI. 8, figs. 5,6) 1973 Racemiguemhelinapowelli Smith and Pessagno: 35-37, pl. 1 I , figs. 4-12. Remarks. According to Smith and Pessagno (1973) R. powelli would differ fromR. fructicosa in having less multiserial chambers, and in possessing bridges instead of sieveplate. They imply that all forms with bridges should be included in R. powelli. As discussed by Nederbragt (1989), Racemiguemhelina specimens may still posses pairs of chambers connected by a microperforate bridge, while resembling R. fructicosa in all other aspects. Here, R. powelli is restricted to those forms with bridges that are not well developed, and have the same wall structure as the actual chambers. Distribution and Range. Here found at Site 605 only, rare throughout the A . mayaroensis Zone.