114 Annals of the South African Museum. 



E. A. Philippi * has figured some Chilian forms (for example, 

 T. arsinoe Philippi, T. foveata Philippi) which may be related to 

 T. van ; they are characterised by great posterior elongation, very 

 convex anterior profile, and two series of ribs on the flank meeting 

 at an angle. The general aspect, indeed, at once suggests the 

 probability of relationship with the two South African types, but the 

 Chilian shells are so unsatisfactorily figured, and their preservation 

 appears to have been so imperfect that further and critical com- 

 parison is not possible. 



Whiteaves has drawn attention to the features wherein Trigonia 

 diver sicostata Whiteaves, f from the Cretaceous of Queen Charlotte 

 Islands, bears resemblance to T. vau. These are : the elongated and 

 posteriorly strongly produced figure of the shell, the convex anterior 

 profile and recurved umbonal region, and the general plan of 

 sculpture on the flank. In T. diver sicostata, however, the anterior 

 ribs are much coarser in character than in T. vau, and are directed 

 almost parallel to the lower valve margin, thus forming a right angle 

 with the posterior ribs instead of an acute angle. A good distinctive 

 feature is seen in the area of the Canadian shell, which is coarsely 

 ornamented by strong longitudinal ribs, and this alone is sufficient 

 to indicate that the two forms are in no way nearly related, but that 

 the common characters of shape and broad plan of flank sculp- 

 ture have been quite independently attained. Whiteaves ascribes 

 T. diver sicostata to the section Scaphoidese, but all members of this 

 division bear evidence of a clavellate ancestry, and longitudinal 

 ornamenting ridges on the area are unknown amongst them. Such 

 ornaments are essentially characteristic of the Costatae, from which 

 T, diversicostata was quite probably derived, and rapid divergence 

 from the typical pattern of the section might well result in this 

 aberrant form, in manner analogous to that exhibited in some of the 

 modified Costatae of the marine Oomia beds in Cutch. T. vau 

 shows no signs of a connection with the section Costatae at any 

 early growth-stage that can be studied, but the ornaments of the 

 area are transverse from the first. 



The peculiarly ornamented Trigonia doroschini Eichwald,J from 

 the Neocomian of Tukusitnu Bay (Alaska), may finally be brought 

 into comparison. This appears to me, however, to be well separated 

 from the group of T. vau (as well as from the group of T. v-scripta 

 in India) by the more truncated and less convex anterior margin and 

 by the manner in which the frontal ribs are directed at right angles 



* E. A. Philippi (1), pis. 34, 35. f Whiteaves (1), p. 68, pi. x., fig. 1. 



J Eichwald (2), p. 180, pi. xiii., figs 12-14; xiv., figs. 1-4. 



