The Invertebrate Fauna of the Uitenhage Series. 35 



ticulars from all known Quadratse, and found that the special features 

 which distinguish this Uitenhage shell from the Jurassic Clavellatae 

 on the one hand and the Cretaceous Quadratae on the other, are 

 shared by Trigonia transitoria Steinm. from Lower Cretaceous rocks 

 in Bolivia, Chili, and the Argentine Eepublic. He therefore sug- 

 gested a new group-name, the Pseudo-quadratae, to comprise these 

 two Trigonia, which were the only examples known to exhibit these 

 peculiar distinguishing characters. Trigonia neuquensis Burckhardt,* 

 which occurs with T. transitoria in Neocomian rocks at Las Lajas 

 on the Eio Agrio (Argentine), falls under the same heading, while 

 T. mamillata t from the Oomia strata in Cutch must also be referred 

 to this group. Still another form, described in these pages (T. holubi), 

 is clearly referable to the same category. Although the five members 

 of the Pseudo-quadratae known to us are all similarly differentiated 

 from the typical Clavellatae, it is not certain that they are all so 

 closely related to one another as might at first sight appear to be 

 the case ; some, at least, may possibly have been independently 

 evolved from clavellate ancestors.]: Nor is it by any means certain 

 that they bear any close and direct relationship to the true Quadratae, 

 and though definite indications on this point fail us, it is quite 

 probable that the Quadratae and Pseudo-quadratae represent parallel 

 and independent groups of derivatives arising from Jurassic Clavel- 

 latae. It is therefore evident that the Trigonia of the group Pseudo- 

 quadratae cannot yet be considered in themselves to furnish quite 

 such reliable guidance to geological age as the true Quadratae, but at 

 the same time their general aspect, by comparison with the Quadratae, 

 strongly suggests a Cretaceous age, while the known South American 

 representatives must, in fact, be regarded as Neocomian. Some of 

 the most important features wherein the Quadratae differ from the 

 Clavellatae are also exemplified in the Pseudo-quadratae. Lycett 

 laid great emphasis on the presence or absence of sculpture on the 

 escutcheon in distinguishing between the Jurassic Clavellatae on the 

 one hand, and the Cretaceous Clavellatae and Quadratae on the other, 

 and in regard to this feature all the Pseudo-quadratae agree with the 

 Quadratae in having coarsely nodose ornamentation on the escutcheon. 

 Further remarks on the points of agreement between these groups 

 are appended to the description of Trigonia holubi, 



Trigonia conocardiiformis (Krauss) was thought by Lycett to fall 



* Burckhardt (2), p. 74, Taf. xiv., figs. 4-6. 

 t Kitchin (1), p. 100, pi. ix., figs. 8, 9 ; pi. x., figs. 1-3. 



I Kemarks on this subject will be found to follow the description and the dis- 

 cussion of the relationships of Trigonia holubi, in these pages. 



