30 EARLY TERTIARY OSTRACODA 



compitalis sp. nov. is larger, lacks well-developed longitudinal ridges and has a ridge 

 running from the eye-tubercle to the subcentral-tubercle. 



Costa (Paracosta) compitalis sp. nov. 



(Plate 14, figs. 3-10) 



Derivation of name. Latin compitalis, pertaining to a cross-roads ; referring 

 to the nexus of the ridges running from the subcentral-tubercle. 



Diagnosis. A large, strongly reticulate species of the subgenus Paracosta in 

 which longitudinal ridges are moderately developed, subcentral-tubercle prominent, 

 joined by three ridges — dorsal, median and a ridge running from eye-tubercle. 



Holotype. Io. 4323, a female carapace (PI. 14, figs. 5, 6, 9, 10). 



Paratype. Io. 4274. 



Material. 14 specimens from the locality below from one horizon (sample 

 no. 3604) . GSP BM 2528-9. 



Type locality. Rakhi Nala section. 



Type Horizon. Upper Chocolate Clays, sample no. 3604. 



Description. Carapace subrectangular in lateral outline. Sexual dimorphism 

 rather pronounced ; the females are shorter and higher than the males. Dorsal 

 margin slightly curved in lateral view because of over-reaching by the dorsal ridge ; 

 ventral margin straight, anterior broadly and evenly rounded, posterodorsal margin 

 very slightly concave, posterior extremity slightly subtriangular, posteroventral 

 margin rounded. Greatest height at anterior cardinal angle, greatest length 

 through the mid-point and greatest width in posterior third. Anterior cardinal 

 angle well-developed with a concavity behind. Left valve slightly larger than right 

 valve, over-reaching at posterodorsal margin and in the region of anterior cardinal 

 angle. Eye-tubercle rounded and distinct and confluent with the anterior marginal 

 rim and a ridge running from the subcentral-tubercle. The prominent subcentral- 

 tubercle lies more or less in the anterior third. Surface coarsely reticulate. There 

 are four longitudinal ridges ; the dorsal ridge commences at the subcentral-tubercle 

 and is curved convexly upward, the median or second ridge stretches back from the 

 subcentral-tubercle towards posteroventral margin, the third ridge slightly slopes 

 upward towards the posterior end and the ventral ridge is almost parallel to the 

 ventral margin and is intercalated between the third ridge and the ventral margin. 

 Anterior and posterior marginal rims distinct. Anterior and posterior margins 

 ornamented with numerous small spines. Internal details not known. 



Dimensions (mm). 



L H w 



Io. 4274 Carapace male 0-98 0-51 0-46 



Io. 4323 Carapace female (holotype) 0-93 0-51 0-44 



Comparison. Costa (Paracosta) disintegrata sp. nov. is smaller than the present 

 species, has ill-defined longitudinal ridges and a carapace tapering towards the 

 posterior end. 



