FROM WEST PAKISTAN 59 



than the females. Anterior margin broadly rounded, posterodorsal margin very 

 slightly concave, posteroventral margin rounded and slightly protracted towards the 

 venter. Dorsal margin straight but appears irregular in lateral view because of the 

 surface ornamentation ; ventral margin nearly straight (concealed in side view by 

 the ventral ridge) . Anterior and posterior cardinal angles well-developed in the right 

 valve but more or less rounded in the left valve. Right valve slightly over-reaches 

 the left at the anterior margin but the left valve over-reaches the right in the region 

 of the posterodorsal slope. Subcentral-tubercle prominent. Eye-tubercle distinct, 

 rounded and glassy. Shell surface deeply reticulate with superimposed papillae or 

 spines, the ornamentation extending onto the prominent ventral ridge (over-reaching 

 the ventral margin in lateral view) which also develops an alar expansion. The 

 posterodorsal process is developed as a short curved horn-like ridge in specimens with 

 papillose ornamentation but is a projecting, blade-like process in specimens having a 

 spinose surface. Anterior and posterior marginal rims distinct. Anterior margin 

 finely denticulate with 20-22 denticles, posteroventral margin with 7-8 short spines. 

 Normal pore canals fairly numerous, one to each reticule. (These become exagger- 

 ated in specimens cleaned in the ultrasonic vibrator). Radial pore canals not very 

 well preserved but appear to be simple, more or less straight, irregularly spaced, 

 some crossing one another, approximately 35 anteriorly. Line of concrescence and 

 inner margin coincide. Dupiicature moderately wide. Selvage prominent — sub- 

 marginal in the left valve but situated in the outer two-fifths of the dupiicature in 

 right valve which also has a deep and well marked anterior and ventral flange groove. 

 Hinge not clearly seen but appears to be holamphidont. 



Dimensions (mm). 



L 

 Io. 4344 Carapace male (holotype) 0-49 



Io. 4258 Carapace female 0-49 



Io. 4295 Left valve female 0-46 



Io. 4296 Right valve female 0-46 



Comparison. Distinguished from the other known species of the genus Phalco- 

 cythere by its small size and the posteroventral margin slightly drawn out towards 

 the venter particularly in the right valve. 



Remarks. The surface ornamentation is variable. Most of the specimens 

 examined have a combination of reticulations and papillae but in a few specimens 

 spines are superimposed on reticulations. 



Phalcocythere rete sp. nov. 

 (Plate 31, figs. 5-12) 



Derivation of name. Latin rete, net ; with reference to the surface ornament- 

 ation. 



Diagnosis. Reticulate Phalcocythere in which eye-tubercle is prominent, ventral 

 ridge present but not prominent, dorsal margin slightly convex particularly in 

 female. 



H 



w 



0-29 



0-27 



0-30 



0-29 



0-28 



— 



0-27 



— 



