The Invertebrate Fauna of the Uitenhage Series. 41 



Costatae from the Jurassic rocks of Europe. These distinguishing 

 features are the elongated oval figure, the delicate sculpture of the 

 marginal carina and area, and the elongated form and fine ornamen- 

 tation of the escutcheon ; they lend an aspect of similarity which 

 cannot be overlooked, especially when these lingering examples of a 

 typically Jurassic section are brought into comparison with the 

 majority of European representatives. 



Other Trigonice which serve in most conspicuous manner to 

 characterise the faunas under consideration, and certainly at first 

 sight appear to furnish the strongest corroborative data in a correla- 

 tion, are the members of the group of Trigonia v-scripta in the 

 Oomia beds and the group of T. vau in the Uitenhage Formation. 

 The similarity of one of the Oomia Trigonice to T. vau Sharpe seems 

 to have been first pointed out by Feistmantel,* and W. T. Blanford t 

 shortly afterwards suggested that a shell from the Oomia Group, 

 which was ascribed by Feistmantel to the genus Goniomya, might in 

 reality represent the African T. vau. Which of three Oomia forms 

 was here and elsewhere J referred to in this connection is uncertain, 

 but it is possibly the one which I have described under the name T. 

 v-scripta, although the less well-known T. dubia in reality bears a 

 much closer resemblance to T. vau, particularly in the outline. 

 When dealing with the Oomia Trigonia I pointed out that T. 

 v-scripta, when adult, more closely approaches an undescribed 

 Uitenhage form which is associated with T. vau. This is T. stowi, 

 described in these pages, and it is certainly closely allied to T. vau ; 

 the youthful characters of shape and ornament are practically 

 identical in these two types, but a marked divergence is observed to 

 accompany progressive growth, and the adult forms are perfectly 

 distinct. The characters of the youthful period in T. v-scripta are 

 also practically the same as in T. recurva, with which it is associated 

 in the Oomia beds, and in this case likewise, wide divergence is 

 exhibited as the adult characters are required. But the marked 

 differences which exist between the essential features in the youthful 

 stage of the two Uitenhage and the two Oomia shells respectively 

 induced me, when describing the Cutch Trigonice, to distinguish 

 between the " Group of T. vau " and the " Group of T. v-scripta." 

 Subsequent examination of further material has strengthened the 

 belief that we are here dealing with a case of convergent development, 

 and that close alliance is by no means to be inferred from the 



* Feistmantel (1), p. 116. f W. T. Blanford (1), p. 118. 



I Medlicott and Blanford (1), p. 261. 



Kitchin (1), p. 70, pis. vii., figs. 6-8; viii., figs. 1-3, 



