34 Annals of the South African Museum. 



it is not distinguishable from the English Lower Cretaceous Serpula 

 that have been variously referred to Serpula filiformis J. de C. So\v, 

 and S. plexus J. de C. Sow. We thus see that in the case of the 

 two Trigonics and the two Serpula which Tate identified with Euro- 

 pean Jurassic types, the determinations were so far erroneous that 

 they are now bereft of the significance which was attached to them 

 as evidence for the age of the fauna. 



We may further examine the evidence for age afforded by some 

 of the more conspicuous bivalves, and firstly I may briefly refer to 

 the representatives of the genus Trigonia, which in themselves lend 

 such a characteristic aspect to the fauna. Although the testimony 

 of these is perhaps not quite so conclusive as Lycett supposed, still, 

 the balance of evidence furnished by members of this genus may be 

 safely relied upon to give a fair indication of age, even when con- 

 sidered apart from associated forms, and the material we are dealing 

 with in the present instance is fortunately of an exceptionally favour- 

 able character. In the first place there is Trigonia ventricosa, 

 T. kraussi, and T. rogersi, all possessing the characters of the section 

 Scabrae a division which, so far as we know, is elsewhere only 

 represented in rocks of Cretaceous age. These might be considered 

 to be balanced by the occurrence of T. tatei, a typical member of the 

 section Costatae, but although this division of the Trigonice has its 

 maximum development in the Oolitic rocks, it is also represented in 

 strata of Lower Cretaceous and even later age. 



Trigonia peninsularis Coquand,* from the Aptian of Spain, cer- 

 tainly shows characters of degeneration not shared by T. tatei, but 

 the Oomia strata of Cutch have yielded two normal representatives 

 of the Costatae, which, together with some degenerate derivatives of 

 this section, are accompanied by Trigonics which exhibit a decidedly 

 Cretaceous aspect. Another unmodified costate form, T. anguste- 

 costata Behr. f occurs in the Argentine Kepublic in strata which 

 are regarded by Behrendsen as Upper Cretaceous, while a typical 

 member of this section has been described by E. Ascher from the 

 Grodischter beds (Hauterivian) of Silesia. J 



Trigonia herzogi (Goldf.), another very characteristic Uitenhage 

 form, was believed by Lycett to belong to the Quadratae, which, so 

 far as known, are exclusively Cretaceous. Steinmann, however, 

 pointed out that Trigonia herzogi differs in several important par- 



* Coquand (1), p. 129, pi. xxiii., fig. 3. 

 f Behrendsen (1), p. 6, pi. 3, fig. 7. 

 J Ascher (1), p. 159 [25], p. xiii. [ii.], fig. 10. 

 Steinmann (2). 



