76 



EARLY TERTIARY OSTRACODA 



less rounded, posterodorsal slope very slightly concave. Dorsal margin straight but 

 appears intricate due to surface ornamentation ; ventral margin slightly concave in 

 front of the middle, particularly in right valve. Greatest height lies in the anterior 

 third, greatest length passes above mid-line. Anterior and posterior cardinal angles 

 well-marked. Valves almost equal. Eye-tubercle distinct and rounded. Subcentral- 

 tubercle prominent and bilobate. Surface ornamentation consists of either tubercles 

 or a combination of reticulations and tubercles. In some cases tubercles become 

 almost spinose. There are three tubercles in the mid-dorsal region and in most 

 specimens these project beyond the dorsal margin in lateral outline. The eye- 

 tubercle is joined to the subcentral-tubercle, by a sharply curved ridge, diagnostic of 

 the genus. The ventral side of the subcentral-tubercle has two weak, short, curved 

 ridges ; one extends towards the anterior and the other towards the posterior end. 

 Anterior marginal rim well-marked, ventral and posterior marginal rims less well- 

 marked. Anterior and posterior margins decorated by short, numerous spines. 

 Posterior has several short spines and two large, somewhat blunt spines, one in the 

 posteroventral corner and the other in the posterodorsal corner. Radial pore canals, 

 simple, almost straight, irregularly spaced, some crossing one another, 25-26 

 anteriorly. Line of concrescence and inner margin coincide. Anterior dupiicature 

 moderately wide, one-twelfth of the entire length of the valve. Selvage pronounced, 

 in right valve it lies in the outer third of the dupiicature but in left valve it is sub- 

 marginal. Right valve with deep ventral and anterior flange grooves. Adductor 

 scars in a vertical column of four. Frontal scar not clearly seen but appears to be 

 oval in shape. Hinge holamphidont with the following details : 



Right valve 



Strongly projecting conical 



tooth. Ocular sinus lies 



below and slightly 



anterior to it. 



Deep socket bounded on 



venter and opening into 



posteromedian groove. 



Locellate groove. 

 Tooth more or less rounded 

 in lateral view but 

 pessular in dorsal view. 



Comparison. Stigmatocythere portentum sp. nov. is larger, than the present 

 species, has three distinct longitudinal ridges, lacks a tuberculate surface and bilobate 

 subcentral-tubercle. Stigmatocythere calia sp. nov. is probably ancestral to 

 S. lumaria but has a vertical posteroventral ridge and more elevated anterior 

 marginal rim. Further, it lacks a tuberculate surface and bilobate subcentral- 

 tubercle. 



This species can be separated into two morphotypes, although it is rather difficult 

 to maintain a distinction between them because of many intermediate forms : 



Element 



Left valve 



Anterior 



Socket bounded on all 





sides, ocular sinus 





opening into it. 



Anteromedian 



Subconical tooth with 





straight anterior and 





convex posterior in 





dorsal view. 



Posteromedian 



Denticulate bar. 



Posterior 



Deep socket open in 





venter. 



