Tlie Invertebrate Fauna of the Uitenhage Series. 143 



delicate, radial, linear striae, which at the lower margin of an adult, 

 and especially in the posterior half of the valve, may be separated by 

 spaces exceeding a millimetre in breadth. The granular ornaments 

 which occur on the striae are delicate though prominent, and widely 

 spaced (nearly 4 mm. apart on the same radial line) towards the 

 lower margin in the posterior half of the valve, but less conspicuous 

 and much more closely spaced in the anterior half." The radial 

 striae leave their impression on the cast when the thin shell becomes 

 removed. 



The well-impressed line on the posterior side of a cast, passes far 

 up and has its angular apex situated close to the umbonal apex. Its 

 anterior limb becomes weakly impressed when traced downwards 

 from the angle for a distance of 7 mm. or 8 mm., and appears to 

 dwindle and disappear at its lower end instead of bending forwards 

 as a well-defined line. On the anterior side of the cast there is 

 a single radial linear impression, less clearly defined than those of 

 the posterior side; it appears most clearly marked at a distance 

 of about 6 mm. from the umbonal apex, and dies out on entering 

 the lower half of the valve. 



Dimensions. (1) (2) (3) 



Length 22 '. 25 . 47mm. 



Height measured from the umbo 19 22 . 30 ,, 



Greatest depth of a single valve ... 8 . 10 . 11 ,, 

 Number (3) is the specimen figured by Sharpe. 



Occurrence. Collected in the railway cutting between milestones 

 24| 24f on the line from Uitenhage to Graaff-Reinet, about three 

 miles from Uitenhage (315) ; also found by Miss M. Wilman at 

 Coega. The locality given by Sharpe is " Zwartkop River." 



Remarks. Sharpe referred this shell with some doubt to the 

 genus Ceromya, and he evidently had not the opportunity of 

 observing the characters of the cast, which would have set at rest 

 all doubts as to a generic determination. In addition to the well- 

 impressed angular line on the posterior side of the umbonal region 

 of the cast, the thin shell and the surface markings afford additional 

 indications of generic position. In the fine specimen collected by 

 Bain and figured by Sharpe, the shell is so preserved that the delicate 

 ornaments of the surface are obscure, and their presence only becomes 

 clearly evident when the specimen is very carefully examined in a 

 good light under slight magnification. The specimen from Coega, 



* It may, perhaps, be more correct to speak of some of these markings as puncta- 

 tions, each of which has a well-raised circular rim ; they represent the bases of very 

 short spines. 



