H 



w 



0-46 



o-37 



o-45 



o-37 



0-49 



o-37 



0-49 



0-42 



FROM WEST PAKISTAN 37 



Dimensions (mm). 



L 

 Io. 4278 Carapace male 0-59 



Io. 4329 Carapace female (holotype) 0-56 



Io. 3131 Carapace male 076 



Io. 3132 Carapace female 0-78 



Comparison. Hemicythere sahnii Tewari and Tandon (i960) appears to be a 

 closely related species. Specimens of this were not available for comparison but 

 from the description and figures given by these authors it does not seem to have the 

 concavity behind the anterior cardinal angle which is present in E(S.) rasilis, sp. nov. 



Remarks. The marginal denticles are not preserved in all specimens. 



Echinocythereis (Scelidocythereis) sparsa sp. nov. 

 (Plate 18, figs. 4, 6, 8, 9) 



Derivation of name. Latin sparsus, scattered ; with reference to the papillae. 



Diagnosis. A species of Scelidocythereis with subrectangular carapace, dorsal 

 margin slightly arched, ventral margin incurved in front of the middle. Surface 

 ornamented with scattered papillae and two ventral ridges. Anterior and posterior 

 marginal rims distinct. Left valve larger than right. 



Holotype. Io. 4330, a female carapace (PI. 18, figs. 8, 9). 



Paratype. Io. 4279. 



Material. 43 specimens from the locality below from three horizons (sample 

 nos. 24159, 24181, and 24183). GSP BM 2539-40. 



Type locality. Zao River section. 



Type horizon. Upper Chocolate Clays, sample no. 24159. 



Description. Sexual dimorphy moderate, the males are longer in proportion 

 than the females. Carapace subrectangular in side view with greatest height at the 

 anterior cardinal angle. Dorsal margin slightly arched, ventral margin sinuated 

 anterior to the middle. Anterior margin broadly rounded, posterior somewhat 

 rounded. Right valve larger than left valve, which it over-reaches along the 

 anterior and ventral margin. Anterior cardinal angle rounded. Sub central-tubercle 

 indistinct, eye-tubercle rounded and distinct. Surface ornamentation consists of 

 sparsely distributed papillae. There are two ventral ridges ; the top ridge bifurcates 

 posteriorly but the bottom ridge is shorter. Anterior and posterior marginal 

 rim fairly well-developed. Anterior margin ornamented with small and numerous 

 denticles, posterior with 6-8 larger denticles. Duplicature moderately wide 

 with a prominent selvage and flange-groove in the right valve particularly in the 

 ventral and anteroventral regions. Radial pore canals simple, almost straight, 

 irregularly spaced, 25-30 anteriorly and 12-15 posteriorly. Hinge holamphidont : 

 right valve with anterior tooth — conical and projecting, followed by postjacent 

 socket, shallow posteromedian groove and posterior reniform tooth. Muscle scar 



