56 



EARLY TERTIARY OSTRACODA 



Element 



Posteromedian 



Posterior 



Left valve 

 Denticulate bar. 

 Deep socket bounded 

 on venter. 



Right valve 

 Locellate groove. 

 Tooth which in dorsal view 

 appears pessular but in 

 reality is semicircular or 

 slightly trilobate. In 

 oblique view it can be 

 seen that the line of 

 concrescence deviates in 

 the neighbourhood of the 

 posterior tooth so that 

 only the outside of the 

 semi-circular tooth is 

 bilamellar thus enclosing 

 a monolamellar core formed 

 by the invagination of the 

 line of concrescence. 



Dimensions (mm). 





L 



H 



w 



Carapace male 



o-8o 



0-44 



0-41 



Carapace female (holotype) 



074 



0-44 



o-39 



Left valve female 



075 



o-45 



— 



Right valve female 



076 



0-44 



— 



Right valve male 



o-8o 



o-45 



— 



10. 3096 

 Io. 4349 



10. 3097 

 Io. 3098 

 Io. 4295 



Comparison. The presence of a reduced ventral ridge, which does not reach the 

 posterior marginal rim, separates this species from Patagonacy there tricostata Hart- 

 mann, Patagonacy there devexa (Muller) and Patagonacy there longiducta antarctica 

 Benson. Patagonacy there tricostata Hartmann (1962) has a smaller and more 

 elongate carapace and three rather than two frontal scars. Patagonacy there devexa 

 (Muller) Benson (1964) is larger, has narrow anterior and posterior vestibules, split 

 adductor scars and ill-defined median and dorsal ridges including the posterodorsal 

 loop. (Comparative material of this species from the British Antarctic region was 

 obtained through the courtesy of Dr. R. C. Whately of Aberystwyth.) Patagona- 

 cythere longiducta antarctica Benson (1964) is about the same size, has a more concave 

 posterodorsal slope and the two median adductor scars are split. 



Remarks. The present species commonly occurs in the Zao River and Rakhi 

 Nala sections, where it has a short vertical range. It is thus a very useful species for 

 correlation in this region. Patagonacy there has so far only been described from cold 

 water regions, but P ? induhis occurs here in a warm water environment. A new 

 generic assignment will therefore probably be necessary at a later time. 



Genus PHALCOCYTHERE nov. 



Derivation of name. Greek phalkes, beam or rib of a ship ; with reference to 

 the ventral ridge + cythere. 



