40 Annals of the South African Museum. 



agreement is the more remarkable from the fact that in seeking 

 additional data for comparative study among the cephalopods of the 

 Oomia beds, the indications of community furnished by the lamelli- 

 branchs are found to obtain no positive support. The cephalopods 

 described by Waagen* from the Oomia Group, with the exception of 

 the belemnites, do not comprise representatives of any of the genera 

 obtained from the Uitenhage beds, and moreover, when brought into 

 comparison with European forms, seemed to Waagen to indicate a 

 Tithonian or Portlandian age. 



Stoliczkaf first directed attention to the great similarity between 

 a Trigonia collected by Wynne during the geological survey of 

 dutch, J and the South African T. ventricosa (Krauss), and the identity 

 of these was afterwards confirmed when the Oomia shell was definitely 

 referred to T. ventricosa by Waagen, Feistmantel, || and W. T. 

 Blanford.li Feistmantel, in 1876,** noted the close similarity be- 

 tween Trigonia herzogi from the Uitenhage beds and a Trigonia from 

 the Oomia Group which I have recently described under the name 

 T. mamillata. As already pointed out, T. mamillata is comparable 

 with T. herzogi and the South American T. transitoria in the manner 

 in which it exhibits characters somewhat intermediate between those 

 of the Clavellatae and the Quadratse, but it bears a still closer 

 resemblance to T. holubi sp. nov. Owing to their large and massive 

 shells, and their well- characterised sculptural plan, the members of 

 this group of Trigonia form a prominent feature in the faunas in 

 which they occur, and supply significant data in the present com- 

 parative study. 



The basis for comparison is further strengthened by the association 

 of true Costatae with members of the Scabrge, both in the Oomia 

 and the Uitenhage strata a fact to which I have already referred. 

 T. parva accompanies T. ventricosa in dutch, and although T. tennis, 

 another costate form, has not been recorded from any of the 

 localities where T. ventricosa is found, it occurs in beds at least not 

 older than those from which the remaining Oomia Trigonia have 

 been obtained. In the Uitenhage Series we have T. tatei, which, 

 although not closely comparable with T. tennis, and distinguished by 

 much coarser ribbing of the flanks, also shares some of the charac- 

 teristics by which the Oomia form is contrasted with most of the 



* Waagen (1). f Stoliczka (2), p, 315 (1871). 



J Wynne (1), pp. 225, 231. Waagen (1), p. 237. 



|i Feistmantel (2), p. 164; (3), p. xxxvii. 



f Medlicott and Blanford (1), p. 261 ; (2), p. 224. See also Kitchin (1), p. 104. 



** Feistmantel (1), p. 116. 



