Fauna and Stratigraphy of the Storrriberg Series. 327 



In a valve having a height of -4 mm. there are 13-14 regularly 

 spaced well-marked fine eostae with broad interspaces. As the valves 

 grow older and larger the eostae increase rapidly in numbers and 

 are crowded together near the ventral border in the larger specimens 

 as in C. mangaliensis. 



The intercostal ornamentation consists of shallow pits when viewed 

 from without and pustules when viewed from within the valve. 

 These are arranged in irregular rows and are set closely together so 

 that there are 7 or 8 rows in each interspace. The pits are rounded 

 rather than polygonal in outline. The older portion of the valve 

 (that around the umbo) is smooth save for the concentric ridges. 

 The pits are more prominent near the ventral, anterior and posterior 

 borders of the valves. The abscence of pits near the umbo on the 

 larger specimens is presumably due to wear or some other cause, 

 as the small specimens occasionally show ornamentation over the 

 whole valve. 



Some of the valves show a considerably greater degree of ribbing 

 than the more typical specimens. This variation in sculpture is 

 paralleled in C. murchisonae in different valves of which Rupert 

 Jones recorded variable ribbing. 



The similarity of ornamentation between the valves of all sizes 

 found at Siberia helps to prove the assumption here made that 

 C. stowiana and C, draperi are but growth-stages of the one species. 

 This possibility was mentioned by Jones X 'Woodward who had not, 

 however, material for observing the intercostal ornamentation on the 

 smaller forms nor intermediate valves showing the gradual changes 

 in size. The variation in shape between specimens of the same size 

 does not seem sufficient warrant for separating the specimens into 

 several species. The species figured by Rupert Jones in his "Monograph 

 of Fossil Estheriae" are variable in shape-characters; and the varia- 

 tions seen in C. draperi are no greater than those figured for his 

 Estheria ovata or E. mintita. 



In general form C. draperi seems to approach fairly closely to 

 C. mangaliensis from the Rhaetic of India and from the Argentine. 



Type. In the British Museum. 



Locality. Harrismith, 0. F. S. 



Horizon. Shale-band in the Cave Sandstone. 



CYZICUS sp. 

 1920. Leriche. Estheria sp. Rev. Zool. Afric. VIII p. 78. PI. II, fig. 1. 



Founded on specimens from the Lubilash Beds at Kitari, canon 

 of the Inzia, Belgian Congo. 



