﻿122 BRITISH FOSSIL TRIGONI^. 



narrow varices separating the area and escutcheon form also a pronainent distinguishing 

 feature. 



Rejecting the comparison with T. aliformis as presenting only remote affinities, there 

 remains the possibility that T. Vectiana of the Neocomian beds (which has been con- 

 founded with T. aliformis) may possibly have formed the subject of comparison. As the 

 Indian species of Forbes appears to have been unknown to the Geological Survey of 

 India, being absent in the Cretaceous species described by Dr. Stolickza, I have been 

 induced to give the following engravings of it, magnified one diameten 



Trigonia Forbesii, Lycett, from Verdachellum, India. 



It will be perceived that the general figure differs from T. Vectiana so considerably 

 that their identity as a species is quite precluded. 



D'Orbigny assigns an American species named aliformis to his T. limhata ('Prodr. de 

 Paleont.,' vol. ii, p. 240, No. 592), and also the Indian species of Forbes. To separate 

 the latter from the species of D'Orbigny it is only necessary to direct attention to the 

 narrow, almost linear area, the produced anterior side, and the curved costae of T. limhata, 

 as depicted in the figures given by D'Orbigny. 



T. aliformis, D'Orbigny (' Pal. Fran.,' p. 143, pi. 291, figs. 1 — 3) is distinct from 

 the British species ; the apices are less elevated and more anterior ; the shell is more 

 produced posteally, having a distinct, plain area, which extends even to the apex ; the 

 costcfi are crossed by a few widely separated sulcations ; they enlarge towards the pallial 

 border throughout all the rows ; they also appear to be destitute of crenulations. 



The Lijrodon aliforme of Goldfuss (' Petref.,' tab. 137, fig. 6, vol. ii) also differs 

 essentially from Parkinson's species in the general figure and the ornamentation 

 of both portions of the shell. The escutcheon has prominent transverse costellse over its 

 entire length, and the other surface of the valve has the costae radiating equally and 

 fringed with closely set, regular, small, bead-like tubercles. 



The T)-i(/onia aliformis of Pictet and Roux (' Gres Vert,' pi. xxxv, figs. 2 a, b) 

 apparently does not differ materially from the species figured by Goldfuss. 



The Trigonia aliformis of Pictet and Renevier (' Terr. Aptien de la Perte du Rhone,' 

 pi. xiv, figs. 1 and 2) : — Fig. 1 is a Blackdown example; fig. 2, from the Rhone, is T. 

 Vectiana, to which the reader is referred. 



