64 EARLY TERTIARY OSTRACODA 



over-reaches the ventral margin in lateral view and is spinose posteriorly. It 

 extends from the anteroventral corner to the posterior third. The posterodorsal 

 process is projecting and blade-like (present in most specimens). Anterior and 

 posterior marginal rims distinct. Anterior margin finely denticulate, posteroventral 

 margin ornamented with 6-7 short spines or papillae. Internal features not seen. 



Dimensions (mm). 



L H W 



Io. 4347 Carapace (holotype) 0-54 0-33 0-44 



Comparison. Phalcocy there sentosa sp. nov. is similar and perhaps ancestral to the 

 present species. These two, however, can be separated easily due to the fact that 

 P. sentosa is strongly dimorphic and has a less well-developed ventral ridge and a 

 posterodorsal process. 



Remarks. This species has so far only been recorded from one horizon of the 

 Upper Chocolate Clays of the Zao River section. Sexual dimorphism has not been 

 observed in this species. 



Phalcocythere sp., cf. P. spinosa 



(Plate 33, figs. 3-6, 9-11) 

 Figured specimens. Io. 4230 — Io. 4232. 



Material. Five specimens from the locality and horizon below (other specimens 

 in the collections of the British Petroleum Co. Ltd., under registration no. FCRM 

 1648). GSPBM2580. 



Locality. Lindi survey, 10-50 ft. above shore at Kitunga, Tanzania. 



Horizon. Upper Eocene. 



Description. Sexual dimorphism rather marked ; the females are higher and 

 wider than the males. Carapace subrectangular to subquadrate in lateral outline. 

 Dorsal margin irregular in lateral view due to ornamentation ; ventral margin almost 

 straight ; anterior margin broadly rounded ; posterodorsal margin very slightly 

 concave ; posterior extremity rounded. Right valve over-reaches the left slightly 

 at the anterior margin. Anterior and posterior cardinal angles well-developed 

 particularly in right valve. Greatest length below mid-point, greatest height at 

 anterior cardinal angle and greatest width in the posterior third. Subcentral-tubercle 

 distinct. Eye-tubercle rounded and prominent. Anterior and posterior marginal 

 rims distinct. Surface ornamentation consists of reticulations with superimposed 

 spines ; ventral ridge prominent, posteriorly alate, ending abruptly in the posterior 

 third ; posterodorsal process prominent and blade-like, standing out in lateral and 

 dorsal views. Anterior margin ornamented with numerous very short spines ; 

 posterior with six larger spines. Radial pore canals not discernible. Duplicature 

 moderately wide. Selvage strong — marginal in left valve but in right valve it is in 

 the outer third. Right valve with a deep flange groove. Muscle scars are in a 

 vertical row of four adductors, and frontal scars not seen. Hinge holamphidont 

 with the details of each element as follows : 



