44 Annals of the South African Museum. 



temporaneous ; and secondly, that the lines of intercourse between 

 the two areas were probably much more direct than was formerly 

 believed to be the case. 



This correlation appears therefore to be in conflict with Waagen's 

 conclusions concerning the age of the marine Oomia beds, which 

 were thought to be Portlandian, but a brief consideration will show 

 that this difficulty is more apparent than real. Doubts might per- 

 haps be expressed as to the validity of a comparison based solely 

 upon lamellibranch types, and it must be admitted that in many 

 similar cases it would be right to place greater confidence in the 

 evidence of cephalopods ; but in the present instance the lamelli- 

 branchs compared are peculiarly well characterised, and indeed com- 

 prise no single form known in the European area. On the soundness 

 of the evidence which these well-marked types afford, and upon which 

 the above conclusions are founded, I think no doubt can reasonably 

 be cast. 



The Mollusca of the marine Oomia beds, shown by Stoliczka to occur 

 in the lower part of the group, cannot be said to give such definite 

 indications of geological age as are to be derived from a study of the 

 Uitenhage fauna. The ammonites from these lower Oomia beds 

 were considered by Waagen to show close affinity with Upper Jurassic 

 forms in Europe, and he believed some of the Trigonics to corroborate 

 fully his view concerning the Portlandian age." But a detailed 

 study of the TriyonicB has shown that this belief was not well founded, 

 and the relationship of any of the Oomia forms to the Portlandian 

 Gibbosae is at the best a matter for conjecture. I have provisionally 

 referred one of these Trigonics to the group Gibbosae on the strength 

 of a certain broad similarity of characters, while at the same time 

 recognising the possibility that this form may represent an aberrant 

 derivative of some costate stock. Judged by analogy with Trigonia 

 retrorsa, which can only be regarded as a degenerate costate type, the 

 relationship of T. spissicostata to the Gibbosae is extremely doubtful, 

 but nothing more definite on this point can be said until material can 

 be collected in a sufficiently favourable state of preservation to throw 

 light on the nature of the youthful stage. Other Oomia Trigonia 

 which exhibit characters simulating those of the Portlandian Gibbosae 

 have been shown to be allied to the section Costataa, and nothing 

 quite comparable with these diversely modified derivatives is known 

 in Jurassic rocks, though the late adult stage of T. peninsnlaris Coq., 

 from the Aptian of Spain, shows an analogous obliteration of sectional 

 features which was regarded by Lycett to indicate degeneracy. The 



* Waagen (1), p. 233 (1875). 



