﻿242 R. Etheridge, Jim. — Contributions to British Palceontology. 



beautiful colour markings preserved on it. In an interesting paper 

 lately published, " On New and Peculiar Mollusca of the Pecten, 

 Mytilus and Area Families procured in the 'Valorous' Expedition," ^ 

 Dr. J. Gwyn Jeffreys, F.K.S., re-defines the genus Amussium as 

 follows : " Shell inequivalve, more or less circular, flattened, smooth 

 or variously sculptured, furnished inside with slight ribs, which 

 radiate from the hinge, and are not impressions of outside markings, 

 but are quite irrespective of them." 



Pecten Sowerbii was referred by Prof. M'Coy in his second de- 

 scription of the shell ^ to the genus Amussium, a reference which is 

 considerably strengthened by the inequality which must exist from 

 the peculiar form of the ears in the two valves, and by the more or 

 less circular or oval flattened form. To complete the analogy we 

 only require the interior radiating ribs, which have not yet come 

 under my own observation in this species. There are also certain 

 analogies with the genus Pseud-amussiwn, to which it has been referred 

 by Prof, de Koninck,^ but even more so with the genus Entolium, 

 Meek. I have lately had an opportunity, through the kindness of my 

 friend Dr. Bigsby, F.E.S., of seeing Hayden's Final Report on the 

 U.S. Geological Survey of Nehraslca, in which Mr. Meek gives a 

 description of Entolium (Pecten) aviculatum, Swallow.^ The genus 

 Entolium was founded by Meek on Pecten demissus, Phill., an Oolite 

 shell possessing a very peculiar hinge structure, well figured by 

 Quenstedt. "I am not sure the group," says Mr. Meek, "is more 

 than sub-generically distinct from Pseud-amussium, Brug. It differs 

 from Amussium mainly in having no internal costae, and in having 

 the valves more nearly equal, with, sometimes, minute radiating 

 striaa, and no traces of a sinus under the anterior ear in either valve. 

 The species known to me have the cardinal margin of the left valve 

 angulated in outline by the elevation of the extremity of the ears, 

 while that of the right valve appears to be straight, and articulated 

 in a little transverse groove of the other valve, not always defined 



however The cartilage pit is as in other allied types of the 



PectinidEe, while diverging from it are two other tooth-like ridges. 

 These, however, do not seem to have been properly teeth, fitting 

 into sockets, but appear to have been a little raised in both valves, 

 and occupy a position between the ears and the broad diverging im- 

 pressions, descending obliquely from the beaks." ^ 



Externally, E. avicidatum is almost identical with our P. Soioerbii, 

 a fact which has not escaped the observation of Mr. Meek ; but I have 

 never as yet seen the above structure in tlie hinge of the latter, and 

 therefore, for the present, 1 refrain from definitely referring P. Soioerbii 

 to Entolium, as Mr. Meek has done.'' The two forms certainly bear 

 a very great resemblance to one another, even to the presence of 

 the V-striee in Entolium. Mr. Meek assigned certain characters on 

 which he based a specific distinction between the two forms, one 

 being the presence of a number of "minute obscure radiating stria3"; 



1 Annals Nat. Hist. 1876, vol. xviii. p. 424. 2 Brit. Pal. Foss. p. 478. 



2 Mon. Foss. Carb. Bleiberg en Carenthie, 1873, p. 94. 



* p. 189. ^ ibid. p. 190. e PL xix. fig. 13. 



