Some species of the genus Neocyprideis in the early Tertiary of Pakistan

Four species of the genus Neocyprideis described in this paper are an addition to the ostracod fauna from the early Tertiary of Pakistan. N. sp. A occurs in the Upper Palaeocene of the Sor Range, and three new species are found in the Eocene of the Sulaiman Range. The new species are Neocyprideis simplex and N. regularis from the upper Lower Eocene, and N. formosa from the uppermost Eocene. The first two species, the associated ostracod fauna and the lithology suggest a shallow marine shelf environment with evaporitic conditions, while N. formosa lived in an open marine shelf environment. The short vertical ranges of these three new species makes them useful stratigraphic markers in this area.


INTRODUCTION
Neocyprideis was established as a subgenus of Cyprideis by Apostolescu in 1956, based upon Cyprideis (Neocyprideis) durocortoriensis from the Upper Palaeocene of the Paris Basin as the type species. It was raised to generic status (by Moore 1961, p. Q277) and van Morkhoven (1963, p. 294). Neocyprideis differs from Cyprideis in having a less complex hinge, fewer radial pore canals, less pronounced sexual dimorphism and in having a less rounded outline in lateral view (van Morkhoven, 1963, p. 295).
The known stratigraphic range of Neocyprideis is late Cretaceous to early Miocene, while Cyprideis ranges from Miocene to Recent. Neocyprideis was a widely distributed genus in the Palaeogene, and has been reported from western and southern Europe, Turkey, Israel, Oman, Pakistan and West Africa (Keen & Racey, 1991).
The four species from Palaeogene sediments that are described in this paper were referred to as Neocyprideis sp. A, B, C, and D in Siddiqui (1971) This paper deals with a small part of the Early Tertiary ostracod fauna from three river sections in Pakistan (Fig. 1). About half of this material has already been described by Siddiqui (1971Siddiqui ( , 1981, and Siddiqui & Al-Furaih (1981). The specimens have been deposited in the Natural History Museum, London.
Terminology used here for the rock units of the Eocene succession of the Rakhi Nala, and which also occur in the northern part of the Sulaiman Range, is that published by Siddiqui (1971, modified from Eames 1952. These units are easily distinguished on the basis of lithology and microfauna.  outline. Sexual dimorphism distinct; the male dimorphs are more elongate, less high and less wide than the females. Both anterior and posterior margins broadly and obliquely rounded. Dorsal margin almost straight in the right valve but slightly convex upwards in the left valve. Greatest height at the anterior cardinal angle. Left valve larger than the right, over-reaching it at almost all the margins. In dorsal view the male and female dimorphs are quite distinct; in the male both anterior and posterior ends are pointed while in the female only the anterior end is pointed. Surface ornamentation variable, smooth, pitted or punctate. Internal details not seen.
This species only occurs in the upper part of the Shale with Alabaster, uppermost member of the Ghajiz Formation, upper Lower Eocene of the Rakhi Nala and Zao River sections.
(PI. 2, figs 3-8) Derivation of name. Latin formosus, beautifully formed; with reference to surface ornamentation. Diagnosis. A species of the genus Neocyprideis with reticulate surface ornamentation except on the dorsal surface; a depression between anterior marginal rim and anterior platform; anterior duplicature fairly wide.

Material.
Four hundred and thirty-nine specimens from the Rakhi Nala section from three horizons (sample nos. 3658, 3663 and 3664). Two hundred and thirty-four specimens from the Zao River section from six horizons (sample nos. 24170, 24180 and 24183, 24191, 24193 and 24195). Type locality and horizon. Rakhi Nala section, Sulaiman Range. Pellatispira beds, Kirthar Formatiom, uppermost Eocene. Description. Sexual dimorphism apparent; the males are more elongate and less wide than the females. Carapace subrectangular in lateral outline with dorsal and ventral margins sub-parallel. Anterior cardinal angle rounded in both valves, but posterior cardinal angle obtuse in left valve and rounded in right valve. Greatest height is at the anterior third of the carapace. Left valve larger than the right valve and over-reaching it at the anterodorsal and posteroventral margins. Shell surface reticulate with rounded fossae; an indistinct sulcus between anterodorsal and mid-dorsal area. Anterior marginal rim distinct with a wellmarked depression posteriorly. Hinge hemi-merodont: left valve with anterior element a loculate groove, median element a loculate bar and posterior element a loculate groove (anterior groove almost twice the length of posterior groove). Right valve complementary. Anterior and ventral duplicature fairly wide with a well-marked subperipheral selvage. Radial pore canals not seen. Normal pores sieve type. Muscle scars consist of a subvertical row of four adductors, a V-shaped frontal scar opening towards the anteroventral margin and an oval-shaped mandibular scar.

Dimensions (pm).
Remarks. The present species shows some resemblance to Miocyprideis paravurensis Khosla 1988 from the Lower Miocene of Kerala, but differs from it in lateral outline and in having a well-marked postero-cardinal angle in the left valve. Miocyprideis fortisensis fortisensis (Keij, 1955) from the Lower Miocene of Moulin de Fortis (Bazadais), as illustrated in 'Atlas des Ostracodes de France' (Oertli, 1985, pl. 91, figs 5, 6), shows some affinity with Neocyprideis formosa sp. nov., but differs from it in having a less pronounced posterocardinal angle in the left valve and a less well-developed anterior marginal rim. This species occurs in the upper part of the Upper Chocolate Clays in both the Rakhi Nala and Zao River sections.

PALAEOECOLOGY
Neocyprideis is closely related to the modern genus Cyprideis, species of which are typically found in brackish to hypersaline waters and some of which develop hollow tubercles in waters of low salinity. Neocyprideis species have also been interpreted as inhabiting a wide variety of low-to high-salinity environments (Keen 1990;Keen & Racey, 1991), and also sometimes developing tubercles in low-salinity environments. These tubercles are generally indicative of less than 5ppt salinity and are most common in juvenile instars. No such tubercles have been found among the four species discussed here. However, two species are found in lithologies indicating evaporitic conditions, and a third occurs at the close of the Eocene Epoch, which was a period of regression.
In the Sulaiman Range, N. simplex and N . regularis are confined to the gypsiferous shales known locally as Shales with Alabaster, uppermost member of the Ghazij Formation, upper Lower Eocene (Fig. 2).
Both these species occur in the Zao River section with such marine ostracod genera as Bairdia, Cytherella, Paracypris, Uroleberis, Xestoleberis, and, the most abundant of them all, the opportunistic Stigmatocythere obliqua Siddiqui 197 1, which flourished in this environment.
In the Rakhi Nala section, N . regularis and S. obliqua thrived together, S. obliqua being again the more abundant; this situation is very similar to the one described by Keen & Racey (1991) from the Lower Eocene, Rusayl Shale of Oman. N. simplex occurs at lower horizons in the Rakhi Nala, with a marine assemblage similar to that of the Zao River but also including Alocopocythere, Eucytherura, Cytherura, Phalcocythere and Schizoptocythere; Stigmatocythere obliqua is sparse at first but increases towards the top of the range.
N . simplex occurs with a marine assemblage in the Shpalai Khwara section.
This distribution suggests shallow marine shelf conditions where gypsiferous sediments were deposited in an evaporitic environment.
N . formosa occurs in the regression phase at the close of the Eocene Epoch in this area. It is found with marine genera

STRATIGRAPHIC OCCURRENCE
The oldest species of this genus recorded from Pakistan is