FROM WEST PAKISTAN 69 



Comparison. Quadracythere (Hornibrookella) arcana (i960) is smaller, has a well- 

 developed caudal process, superimposed longitudinal lineations and a ventral ridge 

 slightly curved downward. Quadracythere (Hornibrookella) platybomus sp. nov. is 

 also smaller, has a different lateral outline, less deep reticulations and an expanded 

 venter. 



Remarks. Quadracythere (Hornibrookella) subquadra sp. nov. commonly occurs 

 at one horizon (sample no. 24161) of the Upper Chocolate Clays in the Zao River 

 section associated with Echinocythereis multibullata sp. nov. and Phalcocythere spinosa 

 sp. nov. 



Quadracythere (Hornibrookella) sp.A 

 (Plate 34, figs. 12-14) 



Figured specimen. Io. 3143. 



Material. Only one specimen from the locality and horizon below. 



Locality. Zao River section. 



Horizon. Upper Chocolate Clays, sample no. 24148. 



Description. Carapace subquadrate in side view. Dorsal and ventral margins 

 almost straight, anterior margin broadly and obliquely rounded, posterodorsal 

 margin slightly concave, posteroventral margin rounded. Greatest length lies below 

 the middle, greatest height at the anterior cardinal angle. In dorsal view the great- 

 est width lies anterior to the middle. Valves almost equal. Eye-tubercle distinct, 

 rounded. Subcentral-tubercle distinct. Surface coarsely and deeply reticulate. 

 Reticulae are somewhat concentrically arranged around the subcentral-tubercle. 

 Dorsal ridge present but not well-defined, ventral ridge more or less distinct. A low 

 marginal rim runs around the anterior and posterior margins. Anterior and postero- 

 ventral margins denticulate. Internal characters not observed. 



Dimensions (mm). 



L H w 



Io. 3143 Carapace 0-93 0-54 0-56 



Comparison. This is similar to Quadracythere (Hornibrookella) subquadra sp. nov. 

 but is much larger, has coarser and deeper reticulations more or less arranged in a 

 concentric pattern around the subcentral-tubercle. In addition, these two species 

 differ markedly in their posterior outline. 



Genus STIGMATOCYTHERE nov. 



Derivation of name. Greek stigma, mark ; with reference to the ornamentation 

 -\-cythere. 



Diagnosis. Highly ornamented Trachyleberididae in which two ridges spring 

 from the eye-tubercle, one to form a high anterior marginal rim, the other curving 

 sharply round to join the subcentral-tubercle. 



Type species. Stigmatocythere obliqua sp. nov. 



