PLATE IV. 



FIGS. 



1. Trifjonia rogersi sp. nov. ... ... ... ... 99 



Dorsal view. Bare slope W. 30 B. from the middle of Barkly 

 JJridge, on the farm Olifant's Kop ('20h). 



2. Triyouia holubi sp. nov. ... ... ... ... ... 103 



2. Left valve ; 2a, frontal aspect of same specimen, showing both 

 valves. Left side of Coega Valley, half a mile down from the 

 railway (458g). In fig. 2, a portion of the shell is missing from 

 the lower part of the valve ; in the drawing, the ribs have been 

 restored in this part and the ornaments supplied by copying the 

 corresponding part of the right valve. 



