36 EARLY TERTIARY OSTRACODA 



posterior end. The posterodorsal process is a short horn-like ridge slightly anterior 

 to the posterior cardinal angle. A marginal rim runs along anterior, venter and 

 posterior margins. 



Dimensions (mm). 



L H W 



Io. 3129 Carapace 0-59 0-39 0-34 



Comparison. This species has already been compared with Echinocythereis 

 (Echinocythereis) contexta sp. nov. 



Echinocythereis (Scelidocythereis) rasilis sp. nov. 

 (Plate 17, figs. 5, 6, 10 ; Plate 18, figs. 1-3, 5, 7) 



Derivation of name. Latin rasilis, smoothed ; with reference to the carapace. 



Diagnosis. Carapace subreniform. Dorsal margin arched with a slight con- 

 cavity behind the protruding anterior cardinal angle. Surface smooth with two 

 ventral ridges. 



Holotype. Io. 4329, a female carapace (PI. 17, figs. 6 ; PI. 18, figs. 2, 3). 



Paratypes. Io. 4278 + Io. 3131-2. 



Material. 17 specimens from the Rakhi Nala section from three horizons 

 (sample nos. 3499, 3614 and 3617). 41 specimens from the Zao River section from 

 seven horizons (sample nos. 24145, 24147, 24148, 24150, 24152 and 24157). GSP 

 BM 2537-8. 



Type locality. Rakhi Nala section. 



Type horizon. Lower Chocolate Clays, sample no. 3499. 



Description. Carapace subreniform in lateral outline, with the greatest height 

 at the anterior cardinal angle. Dorsal margin arched with a slight concavity behind 

 the anterior cardinal angle, ventral margin incurved anterior of the middle, particu- 

 larly in the right valve ; anterior margin broadly rounded, posterodorsal slope very 

 slightly concave, posterior extremity rounded, posteroventral margin curved or 

 straight. In dorsal view the greatest width lies almost at the middle. Anterior and 

 posterior marginal areas compressed. Anterior cardinal angle protruding, Right 

 valve over-reaches left valve along the anterior and posteroventral margins. Left 

 valve over-reaches right valve slightly in the regions of the anterior cardinal angle 

 and posterodorsal slope. Surface smooth. There are two ventral ridges, the one 

 nearest the ventral margin being smaller. Eye-tubercle more or less distinct and situ- 

 ated below the anterior cardinal angle. Anterior margin finely denticulate (20-25 

 small denticles), posterior with 6-8 larger denticles. Duplicature fairly wide, 

 0-073 mm. anteriorly. In the right valve the selvage and flange groove are well- 

 developed particularly in the anteroventral and ventral regions. In the left valve 

 the selvage is well-marked but the flange groove is somewhat less well-developed. 

 Radial pore canals not clearly visible but would seem to be simple, straight and 

 numerous. No vestibule. Hinge not determinable. 



