﻿QUADRATE. 



Ill 



from Ventoux figured by D'Orbigny (' Pal. Fran.,' pi. 289, fig. 5), but the characters of 

 the surface are obscure, and do not afford an adequate idea of the species. 



The very characteristic figures given by D'Orbigny ('Paleont. Fran., Terr. Cret.,' 

 Atlas,' torn, iii, plate 289, figs. 1 — 5) represent three Neocomian Trigonise of differing 

 aspects, which are intended as illustrative figures of T. rudis, Park. ; T. nodosa, Sow. ; 

 T. spectabilis, Sow. ; T. cincta, Ag. ; and T. palmata, Desh. The specimen figs. 1, 2 

 has affinities with certain ill-preserved examples of T. nodosa, from the coarse sandstone 

 at Hythe, in the more horizontal direction of the rows of pallial varices, and in the great 

 length of the siphonal border ; two imperfect specimens in Mr. Sowerby's collection, 

 mentioned by him in the ' Mineral Conchology,' now in the British Museum, illustrate 

 these features; also our specimen from the lowest or Perna bed at Redcliff, Sandown 

 Bay, excepting that the figure is more lengthened. Fig. 5, from Ventoux, has affinities 

 with our Tealby specimen in the surface of the area and in the rows of small pallial 

 varices with their rounded nodes, but differs in the ornamentation upon the position of 

 the marginal carina ; the T. cincta of Agassiz also approximates to the Ventoux variety. 

 Figs. 3, 4 are strictly identical with the more common aspect of specimens from the beds 

 of Crackers, Isle of Wight, which 1 have distinguished as T. Orbignyana. None of 

 the figures present even a remote approximation to T. spectabilis, Sow., or to T. palmata, 

 Desh. The former of these is the species next described ; the latter is referred to as a 

 variety of 7! dcedalea ; neither of them occurs in the Neocomian formation. 



Our variety Orbignyana is well exemplified by the shell figured for T. dcedalea by 

 Pictet and Renevier (' Foss. du Terr. Aptien de la Perte du Rhone,' plate 12, fig. 1), which 

 offers no material difference when compared with the Atherfield specimens. Their 

 example of T. nodosa, fig. 2 upon the same plate, differs so materially from all varieties of 

 the species, whether British or foreign, that it cannot be accepted as pertaining to that 

 species. The escutcheon in the present shell is so large, both in length and breadth, that 

 when we find it furnished with a numerous series of regular transverse costellse, which are 

 visible even when the shell is laid upon its side, it is impossible to associate it with the 

 narrow form, horizontal surface, and crowded, obliquely nodose varices which characterise 

 the escutcheon in T. nodosa ; the unusually lengthened form, the row of rounded nodes 

 upon the whole length of the median carina, together with the short perpendicular rows 

 of equal nodes upon the pallial portion of the valve, are equally distinctive ; they also 

 separate it from a large, imperfect, clavellated Trigonia figured by Pictet and Roux 

 (' Gres Vert,' plate xxxv, fig. 5) for T. nodosa, in which the rounded nodes in the rows 

 become symmetrically small and inconspicuous as they approach the area ; they even pass 

 across the area in an attenuated form. The general aspect of this species would associate 

 it with the Clavellata, but as the limits of the area are not clearly defined, as it is without 

 bounding carina?, and as some of the rows of nodes pass across it, it should apparently be 

 arranged with the Quadrata. The escutcheon is not seen. 



Foreign Localities. — The small examples of T. nodosa or T. cincta figured by 



