FROM WEST PAKISTAN 81 



Remarks. T. (A.) procapsus has so far only been recovered from the Upper 

 Palaeocene of the Sor Range section. 



Trachyleberis (Acanthocythereis) usitata sp. nov. 



(Plate 41, figs. 2, 5, 7) 



Derivation of name. Latin usitatus, usual. 



Diagnosis. Carapace tapering towards posterior. Subcentral-tubercle distinct. 

 Surface reticulate with superimposed pustules and a posterodorsal process. 



Holotype. Io. 4362, a male carapace (PI. 41, fig. 2). 



Paratype. Io. 3161. 



Material. Five specimens from the Rakhi Nala section from four horizons 

 (sample nos. 3111, 3130, 3132 and 3133). GSP BM 2599. 



Type locality. Rakhi Nala section. 



Type horizon. Gorge Beds, sample no. 3111. 



Description. Sexual dimorphy present ; the males are longer in proportion to 

 the females. Carapace elongate, subrectangular, tapering towards the posterior. 

 Anterior margin broadly rounded, posterior narrowly rounded. Dorsal and ventral 

 margins almost straight. Greatest height at the anterior cardinal angle which is 

 well-developed in the left valve. Greatest length passes through mid-point. Valves 

 almost equal. In dorsal view greatest width lies in the anterior third (in the region 

 of the subcentral-tubercle). Eye-tubercle rounded and distinct. Subcentral-tubercle 

 fairly distinct. Anterior and posterior marginal rims sharply defined. Surface 

 reticulate with pustules at reticulae intersections. A posterodorsal process in the 

 form of more or less rounded tubercle of medium size present. A double row of 

 pustules decorates anterior and posterior margins. Internal characters not known. 



Dimensions (mm). 



L H W 



Io. 4362 Carapace male (holotype) 0-63 0-32 — 



Io. 3161 Carapace female 0-59 0-32 0-22 



Comparison. This species shows some resemblance to Trachyleberis {Acantho- 

 cythereis) decoris sp. nov. but is smaller, has marginal pustules rather than spines and 

 carapace more tapering towards the posterior. Trachyleberis (Acanthocythereis) 

 postcornis has a characteristic posterodorsal process, more high marginal rims and 

 spinose anterior and posterior margins. 



Remarks. In some specimens the posterodorsal process is not well-developed. 



Trachyleberis (Acanthocythereis) pedigaster sp. nov. 



(Plate 41, figs. 6, 8) 



Derivation of name. Greek pedigaster, flat belly ; with reference to the ventral 

 inflation. 



Diagnosis. A large species of the subgenus with ventral inflation. Carapace 

 tapering towards posterior. Posterior margin subtriangular. 



F 



