L 



H 



W 



o-39 



0-20 



0-13 



o-37 



0-20 



0-13 



FROM WEST PAKISTAN 53 



MORPHOTYPE E 



(PI. 27, figs. 7-12) 

 This is very similar to Morphotype B, but has a wedge-shaped carapace. 

 Dimensions (mm). 



Io. 3137 Carapace male 

 Io. 3138 Carapace female 



Occultocythereis indistincta sp. nov. 

 (Plate 27, figs. 13-15 ; Plate 28, figs. 1-4) 



Derivation of name. Latin indistinctus, dim or obscure ; named from the 

 absence of well-marked diagnostic characters. 



Diagnosis. A species of the genus Occultocythereis with a well-developed dorsal 

 ridge ending posteriorly in a large subangular posterodorsal process, ventral ridge 

 oblique running from anteroventral corner towards posterior, surface ornamentation 

 consists of indistinct puncta. 



Holotype. Io. 4340, a female carapace (PL 27, figs. 15 ; PL 28, figs. I, 3, 4). 



Paratypes. Io. 4294 + Io. 3135. 



Material. 44 specimens from the locality below from seven horizons (sample 

 nos. 3499, 3614, 3615, 3621, 3625, 3648 and 3649). GSP BM 2566-7. 



Type locality. Rakhi Nala section. 



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



Description. Sexual dimorphism apparent ; the males are more elongate, less 

 high and less wide than the females. Carapace subrectangular, slightly tapering 

 towards the posterior. Dorsal margin straight but irregular in side view due to the 

 over-reaching of the dorsal ridge, ventral margin almost straight, anterior margin 

 broadly and evenly rounded, posterior narrow, subangular in the middle with 

 slightly concave posterodorsal slope. Greatest length lies in the middle, greatest 

 height in the anterior third. Anterior cardinal angle well-developed particularly in 

 left valve, posterior cardinal angle rounded in the right valve but pointed in left 

 valve. Left valve over-reaches right valve in the region of anterior cardinal angle 

 and posterodorsal slope. Eye-tubercle distinct. Surface ornamented with small, 

 indistinct puncta. Anteromedian swelling (which perhaps represents a subcentral- 

 tubercle) distinct. A well-marked dorsal ridge commences behind the eye-tubercle 

 and is slightly convex upward in the middle terminating in a large subangular 

 posterodorsal process. In most specimens it is ornamented with three small tubercles 

 which lie at some distance from one another. Ventral ridge runs obliquely from the 

 anteroventral corner towards the posterior, culminating in the posterior third. (In 

 some specimens it is not well-developed) . A small tubercle is present in the postero- 



