88 EARLY TERTIARY OSTRACODA 



Ostracod Biostratigraphic Unit V , Middle-Upper Eocene 



The biostratigraphic Unit V of the Rakhi Nala section occurs in the Zao River and 

 is 3743 ^. thick. The Unit includes the Platy Limestone, Lower Chocolate Clays 

 and both lower and upper parts of the Upper Chocolate Clays. The Pellatispira 

 Beds have not been recorded in the Zao River section. The bottom 460 ft. of the 

 Unit comprising the Platy Limestone and the lower part of the Lower Chococlate 

 Clays and the top 600 ft. of the upper part of the Upper Chocolate Clays have not 

 yielded any ostracods and are only provisionally included in the Unit. 



The Unit is very rich in well-preserved ostracods. The ostracod fauna is com- 

 pletely new since none of the species from the Unit below survive. There are 7% 

 of the species which are restricted to the upper part of the Lower Chocolate Clays ; 

 26% have only been found in the lower part of the Upper Chocolate Clays ; and 17% 

 have been recorded from the upper part of the Upper Chocolate Clays only. 24% of 

 the species occur in the upper part of the Lower Chocolate Clays and the lower part 

 of the Upper Chocolate Clays ; 13% range from the upper part of the Lower Choco- 

 late Clays to the upper part of the Upper Chocolate Clays and 41% are shared be- 

 tween the lower and upper parts of the Upper Chocolate Clays. 



The ostracod fauna of the Unit in the Zao River section is very similar to that of 

 the Rakhi Nala section. It has about 74% of its species in common with the Rakhi 

 Nala. These are shown in Appendix 2. As in the Rakhi Nala, Alocopocythere is 

 one of the commonest genera and it occurs in great abundance at several horizons. 

 It is represented by three related species ; A. transcendens sp. no v., A. transversa 

 sp. nov. (with six morphotypes), and A. radiata sp. nov. Stigamatocythere is another 

 common genus and has three species in the Unit : S. calia sp. nov., 5. delineata 

 sp. nov. and 5. lumaria sp. nov. (with two morphotypes). Among these, 5. lumaria 

 is the commonest, occurring in the lower and upper parts of the Upper Chocolate 

 Clays. S. calia and S. delineata have so far not been found in the Rakhi Nala section. 

 Bairdoppilata sp.A, Pterygocythereis (Pterygocythere) sp.A are more common in the Zao 

 River section. Trachyleberis (Acanthocythereis) decoris sp. nov. and Cytheromorpha 

 sp.A, which were very common in the Rakhi Nala are rare in the Zao River. The 

 subgenus Paracosta nov. which is represented by three species in the Rakhi Nala has 

 not so far been recorded from the Zoa River. Phalcocythere spinosa sp. nov. and 

 Quadracythere (Hornibrookella) subquadra sp. nov. have only been found in sample 

 24161 of the Zao River section, where they occur in association with the larger 

 foraminifera Pellatispira orbitoidea. Some of the more important members of the 

 unit are : Alocopocythere transcendens sp. nov., Alocopocythere transversa sp. nov., 

 Bairdoppilata sp.A, Cytherelloidea cf. C. costatruncata Lubimova and Mohan, 

 Patagonacy there ? nidulus, sp. nov. and Stimatocy there lumaria sp. nov. 



Shpalai Khwara Section 



The ostracod biostratigraphic Unit IV of the Rakhi Nala and Zao River sections 

 is also represented in the Shpalai Khwara section. 





