EARLY TERTIARY OSTRACODA 



Diagnosis. Medium size, thick shelled. High and distinct anterior marginal 

 rim with posterior ornamentation. Surface sparsely punctate. Subcentral tubercle 

 prominent and rounded. 



Holotype. Io. 4311, a female carapace (PI. I, Figs. 2, 3, 11, 12). 



Paratypes. Io. 4260 + Io. 3100-1. 



Material. 29 specimens from the Rakhi Nala section from 8 horizons (sample 

 nos. 3610, to 3615, 3617, 3618 and 3620). 10 specimens from the Zao River section 

 from two horizons (sample nos. 24150 and 24154). GSP BM 2506-7. 



Type locality. Rakhi Nala section. 



Type horizon. Upper Chocolate Clays, sample no. 3611. 



Description. Sexual dimorphy moderate, the females are higher and wider than 

 the males. Carapace sub-rectangular, medium size and thick shelled. Anterior 

 margin broadly rounded, postero-dorsal margin slightly concave, posterior extremity 

 and postero-ventral margin somewhat rounded. Dorsal and ventral margins almost 

 straight, slightly tapering towards the posterior. In lateral view the dorsal orna- 

 mentation over-reaches the dorsal margin. Valves almost equal. In dorsal view 

 the greatest width passes through the sub-central node. Eye-tubercle rounded, 

 prominent and situated below and slightly anterior to a well-developed anterior 

 cardinal angle. Anterior marginal rim high. Ventral and posterior marginal rims 

 less high. Sub-central tubercle prominent, rounded and distinct. Surface sparsely 

 punctate (punctation is not distinct in some specimens), with an alate ventral ridge 

 which slightly slopes upwards towards the posterior. The postero-dorsal process is 

 a blade-like projecting ridge over-reaching the dorsal margin and extending vertically 

 below for a short distance. A prominent mid-dorsal tubercle with a small tubercle 

 present in front. There is also a small tubercle posterior and at some distance from 

 the sub-central node. About 12 short marginal spines anteriorly, partly concealed 

 in external lateral view by the anterior marginal rim, and 5-6 spines posteriorly. 

 Radial pore canals few, simple and straight. Inner margin and line of concrescence 

 coincide. Duplicative moderately wide. Selvage well marked lying sub-peripheral 

 in left valve, but at some distance from the outer margin in right valve. There is a 

 fairly well-developed flange groove in right valve. Muscle scars unknown. Hinge 

 holamphidont with the details given below : 



Left Valve 



Socket 



Subcorneal tooth 



having a straight 



anterior and a convex 



posterior in dorsal 



view 



Denticulate bar 



Slightly elongate 



socket, open on 



venter. 



Hinge element 



Anterior 



Anteromedian 



Right Valve 



Conical projecting tooth 



Deep socket 



Posteromedian 

 Posterior 



Shallow locellate groove 

 Pessular tooth 



