FROM WEST PAKISTAN 31 



Costa (Paracosta) disintegrata sp. nov. 



(Plate 14, figs. 11 ; Plate 15, figs. 1-6) 



Derivation of name. Latin disintegratus, " broken down " ; referring to the 

 relict nature of the ridges characteristic of Costa. 



Diagnosis. Paracosta of medium size with weakly developed longitudinal ridges. 

 Carapace tapering towards posterior end in lateral view. 



Holotype. Io. 4324, a male carapace (PL 14, figs. 11 ; PL 15, figs. 3, 4). 



Paratype. Io. 4275. 



Material. Four specimens from the locality below from two horizons (samples 

 no. 3621 and 3622). GSPBM 2530-31. 



Type locality. Rakhi Nala section. 



Type horizon. Upper Chocolate Clays, sample no. 3622. 



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

 than females. Carapace subrectangular, tapering to posterior in side view. Dorsal 

 and ventral margins almost straight, anterior margin broadly and evenly rounded, 

 posterior subtriangular. Anterior cardinal angle rounded, posterior cardinal angle 

 obtuse — well-developed in left valve. Left valve over-reaches the right slightly at 

 the anterior cardinal angle and in the region of the posterodorsal slope. A distinct 

 eye-tubercle lies just below the anterior cardinal angle. Subcentral-tubercle well- 

 developed. Anterior and posterior marginal rims high. Surface coarsely reticulate 

 (some reticulae being slightly papillose). There are four ill-defined longitudinal 

 ridges ; the dorsal ridge commences just behind the subcentral tubercle and is curved 

 convexly upward ; the second ridge stretching back from the subcentral-tubercle 

 towards the posterodorsal corner in the anterior two-thirds and then bends sharply 

 round towards the posteroventral corner ; the third ridge commences below the 

 subcentral-tubercle and slopes upward towards the posterior end ; the fourth ridge 

 (better seen in ventral view) is more or less parallel to the third ridge and lies between 

 the ventral margin and the third ridge. Anterior and posterior margins spinose. 



Dimensions (mm). 



L H W 



Io. 4275 Carapace male 0-83 0-42 0-32 



Io. 4324 Carapace female (holotype) 0-85 0-44 0-37 



Comparison. This species falls between Costa (Paracosta) compitalis sp. nov. and 

 Costa (Paracosta) declivis sp. nov. in size and stratigraphical position and has already 

 been compared with these species. 



Genus ECHINOCYTHEREIS Puri 1954 



Diagnosis. Trachyleberididae with or without ventral ridges. Carapace often 

 inflated and with curved posteroventral margin, particularly in right valve. Surface 

 ornamented with papillae, nodes, reticulations (or combination of these — con- 



