FROM WEST PAKISTAN 33 



Echinocythereis (Echinocythereis) elongata sp. nov. 

 (Plate 15, figs. 9, u, 12, 14 ; Plate 16, figs, i, 2) 



Derivation of name. Latin elongatus, elongate ; with reference to the carapace. 



Diagnosis. An elongate species of the subgenus Echinocythereis in which posterior 

 end is rounded towards posterodorsal corner, subcentral-tubercle distinct, surface 

 ornamented with reticulae and papillae. 



Holotype. Io. 4327, a female carapace (PL 15, figs. 12, 14 ; PL 16. fig. 1). 



Paratype. Io. 3130. 



Material. Nine specimens from the Rakhi Nala section from three horizons 

 (sample nos. 3404, 3409 and 3416). GSP BM 2534. 



Type locality. Rakhi Nala section. 



Type horizon. Rubbly Limestones, sample no. 3416. 



Description. Carapace elongate, subrectangular in lateral outline. Sexual 

 dimorphism rather prominent in dorsal view ; males longer and less wide than females. 

 Anterior margin broadly rounded, posterior narrowly rounded towards postero- 

 dorsal corner particularly in the left valve, dorsal margin irregular due to ornamenta- 

 tion, ventral margin more or less straight. Greatest length lies above the middle, 

 greatest height at the anterior cardinal angle and greatest width in front of the 

 middle. Valves almost equal. Subcentral-tubercle distinct. Eye-tubercle fairly 

 distinct, but worn in some specimens. Surface ornamentation a combination of 

 reticulations and papillae. The reticulae are in the anterior and ventral regions and 

 the papillae in the middle and posterior. The papillae are perhaps revealed by the 

 removal of an upper layer of reticulae. The decorated papillae show normal pore 

 canals and nexus of reticulae, which are smaller than the anterior and ventral ones. 

 Normal pore canals are situated between the papillae. Anterior and posterior 

 margins denticulate, although the denticles are not preserved in some specimens. 

 Internal characters unknown. 



Dimensions (mm). 



L H W 



Io. 3130 Carapace male 0-73 0-39 0-29 



Io. 4327 Carapace female (holotype) 0-71 0-38 0-34 



Comparison. This species can easily be separated from the other known species 

 of the subgenus Echinocythereis by its much more elongate carapace-. 



Subgenus SCELIDOCYTHEREIS nov. 



Derivation of name. Greek skelis, rib ; with reference to the development of 

 the ventral ridges. 



Diagnosis. Echinocythereis with ventral ridges. 



c 



