84 EARLY TERTIARY OSTRACODA 



tions with superimposed pustules. Carapace subrect angular with dorsal and ventral 

 margins almost straight and subparallel. 



Holotype. Io. 4359, a male carapace (PI. 42, figs. 3, 4, 5). 



Paratype. Io. 4310. 



Material. Over 250 specimens from the type locality from 18 horizons (sample 

 nos. 3604, 3607, 3610, 3613 to 3615, 3629, 3640, 3642, 3645, 3648 to 3650, 3661 to 

 3664). 7 specimens from the Zao River section from 3 horizons (sample nos. 24154, 

 24173 and 24193). GSPBM 2601-2. 



Type section. Rakhi Nala section. 



Type horizon. Upper Chocolate Clays, sample no. 3640. 



Description. Sexual dimorphism rather marked ; the males are longer in pro- 

 portion than the females. Carapace subrect angular in lateral view with dorsal and 

 ventral margins almost straight and subparallel. Anterior margin broadly and evenly 

 rounded, posterior slightly subtriangular. Both anterior and posterior margins 

 ornamented by a double row of short spines, the posterior ones being larger. Anterior 

 cardinal angle rounded, posterior cardinal angle well-marked. Greatest height at the 

 anterior cardinal angle and greatest length in the middle. In dorsal view greatest 

 width lies in the anterior third. Valves almost equal. Surface reticulate with super- 

 imposed pustules. Eye-tubercle rounded and distinct. Subcentral-tubercle more or 

 less distinct (better seen in slightly worn specimens). A large number of specimens 

 (particularly the females) show development of postero ventral prominence. In a few 

 specimens a small posterodorsal process also develops, but these characters here are 

 regarded as variations within the species. Dupiicature fairly wide with a submarginal 

 selvage. Radial pore canals not seen. Muscle scar pattern consists of four adductors 

 in a vertical superposition at the posterior margin of the muscle scar pit with a 

 U-shaped frontal scar opening towards the anterodorsal corner. Hinge holamphidont : 



Element Left valve Right valve 



Anterior Socket. Slightly stirpate tooth. 



Anteromedian Subcorneal tooth. Denticulate ridge. 



Posterior Deep socket. Somewhat rounded tooth 



in lateral view. 



Dimensions (mm). 



L H w 



I°- 4359 Carapace male (holotype) 0-67 0-32 0-24 



Io. 4310 Carapace female 0-59 0-32 0-23 



Comparison. In some respects this species resembles Trachyleberis (Acantho- 

 cythereis) procapsus sp. nov., but differs in lacking the smooth walled area enclosed 

 by the anterior marginal rim and compressed anterior and posterior marginal 

 platforms. These two species also differ in size, T. (A.) decor is being smaller, higher 

 and wider in proportion than T. (A.) procapsus. 



Remarks. This species commonly occurs in the Upper Chocolate Clays of the 

 Rakhi Nala section but it is very rare in the Zao River section. 



