86 EARLY TERTIARY OSTRACODA 



This is the first Eocene ostracod assemblage. It is fairly rich and at several 

 horizons the ostracods are very abundant. None of the Palaeocene species survive 

 and a completely new fauna evolves. The ostracod fauna is of changing suite ; 

 species appear and disappear in the unit, but there seems to be no major break of 

 any kind in the fauna. Trachyleberis (Trachyleberis) lobuculus sp. nov., Gyrocythere 

 parvicarinata sp. nov., Occultocythereis peristicta sp. nov. (with five morphotypes), 

 Schizocythere sp.A and Pontocythere sp.A are the most important members restricted 

 to the unit. Approximately 50% of the species range up into the overlying Unit IV. 



Ostracod Biostratigraphic Unit IV, Lower Eocene {upper part) 



This consists of the Shales with Alabaster and includes Eames' local zone 7. It has 

 a very rich ostracod faunal assemblage. Most of the samples studied were extremely 

 rich in ostracods, which are mostly complete carapaces. The most typical species 

 confined to the unit are Stigmatocyihere obliqua sp. nov., Phalcocythere dissenta sp. nov. 

 Genus C sp. 1 and Genus C sp. 2. More than 50% of the species are restricted to the 

 unit, although approximately 44% are common to Unit III, and only one species 

 ranges up into Unit V. 



Ostracod Biostratigraphic Unit V , Middle— U pper Eocene 



This comprises the Platy Limestone, Lower Chocolate Clays, Upper Chocolate 

 Clays and Pellatispira Beds. Eames' local zones 8 to 15 and Latif's top six pelagic 

 foraminiferal zones occur in this unit. The lowest 730 ft., which form the Platy 

 Limestone and most of the Lower Chocolate Clays, excluding the top 30 ft., are 

 devoid of any recognizable ostracods and are provisionally included in the unit. 

 There are 200 ft. of covered sediments in the Lower Chocolate Clays below sample 



3494- 



The Unit is very rich in very well-preserved ostracods. It differs markedly from 

 the underlying Unit. All the species except Alocopocythere transcendens sp. nov., 

 which survives from the Unit below, appear for the first time, although a few have their 

 ancestors in the Unit IV. The first appearance of ostracods in the Unit is in the 

 uppermost part of the Lower Chocolate Clays (sample nos. 3498 and 3499), which lies 

 at the base of the Globigerina yeguaensis zone of Latif. The ostracod fauna is varied 

 and of changing suite. 12% of the species are restricted to the Lower Chocolate 

 Clays (topmost portion) ; 25% are confined to the Upper Chocolate Clays (lower 

 part) ; and only 8% have been recorded from the Pellatispira Beds. 33% of the 

 species are shared between the Lower Chocolate Clays (topmost portion) and Upper 

 Chocolate Clays (lower part) ; 17% range from the Lower Chocolate Clays (upper- 

 most part) to the Upper Chocolate Clays (upper part) ; 37% are shared between the 

 Upper Chocolate Clays (lower part) and Upper Chocolate Clays (upper part) ; 8% 

 range from the Upper Chocolate Clays (lower part) to the Pellatispira Beds ; and 12% 

 are found in both the Upper Chocolate Clays (upper part) and Pellatispira Beds. 

 (The percentages are approximate and are based on the entire ostracod fauna of the 

 Unit). 



The genus Alocopocythere nov. occurs abundantly almost throughout the Unit. 



