﻿SCABRtE. 121 



author in tlie ' Nova Acta,' above quoted ; it is an abnormal, depressed, and altogether very- 

 peculiar example of the Clavellafce, and is only very remotely allied to any other known 

 species of that section. Its general aspect has some resemblance to a lengthened 

 Pholadovii/a ; its hinge characters are well exposed, otherwise it might be mistaken for 

 another genus. The Clavellata; although eminently Jurassic, are not exclusively so, as 

 the section is represented in British Neocomian rocks by two species. 



The supposed presence of T. aliformis in the Cretaceous rocks of India referred to by 

 Von Buch is founded upon a memoir by Professor E. Forbes on Cretaceous fossils from 

 the hiU of Verdachellum, south-west of Pondicherry (' Geol. Trans.,' 2nd series, vol. 

 vii, part 3, p. 151). The liberality of the Geological Society in granting to me the 

 loan of the Trigonm from Verdachellum upon which the observations were grounded has 

 enabled me to compare them carefully with British species ; the results are as 

 follow : — 



Six specimens representing species named T. semicuUa, T. suborbicularis, and T. 

 orientalis, are examples of the Glahrce, and differ from any known European forms ; 

 apparently the two latter species should be merged in one ; they are sufBciently figured 

 in the plates which accompany the memoir. 



The Indian supposed representative of T. aliformis is founded upon a single small 

 example of the Scabra, which, when perfect, would be abovit 12 lines in length, but the 

 posteal portion is broken away, which reduces the length to 'd\ lines, in a matrix of 

 reddish-brown, concretionary rock. A delicate valve of a small Placunopsis lies across- 

 the area and escutcheon, the surfaces of which, however, are not obscured by the 

 parasitic valve. A mere first glance is sufficient to assure us that the comparison could not 

 have been made with any British example of T. aliformis, and that the Indian species 

 cannot even be arranged as a variety of that form. The figure not less than the orna- 

 mentation is distinct ; it has nothing of the posteal flattening and sudden anteal inflation 

 which is so characteristic of Parkinson's species, no separation of the costse into two kinds, 

 viz. the small, perpendicular posteal, contrasted with the oblique anteal, inflated mesially, 

 with their delicate, almost evanescent crenulations. On the contrary, the contour of the 

 surface is uniform, and the costse are all of one kind, narrow, elevated, and straight for 

 the most part, but having a few of the first-formed curved towards the anterior border ; 

 all are fringed with large, obtuse, prominent, irregular, and unequal nodes, but the few 

 first-formed or unibonal rows have the little nodes or tubercles regular and bead-like ; all 

 are united to the angle of the valve, which forms a distinct, narrow-knotted ridge. The 

 area and escutcheon are together large and concave ; the area, much wider than in 

 any British species of the alformis group, has transverse costellse conformable in 

 number with the costas ; they are large and suddenly form a row of prominent narrow 

 varices, which separate the area from the more depressed and concave escutcheon, across 

 which the costellae also pass in a more attenuated form. The whole of these features 

 differ essentially from the corresponding parts in T. aliformis ; and the border of elevated 



