242 R. Ethcridge, Jun. — Contributions to British Palceontotogy. 
beautiful colour markings preserved on it. In an interesting paper 
lately published, “ On New and Peculiar Mollusca of tbe Beeten, 
Ihjtilus and Area Families procured in tbe ‘ Yalorous ’ Expedition,” 1 
Dr. J. Grwyn Jetfreys, F.R.S., re-defines tbe genus Amussium as 
follows : “ Shell inequivalve, more or less circular, flattened, sraootli 
or variously sculptured, furnisbed inside witb sligbt ribs, wbicli 
radiate from tbe hinge, and are not impressions of outside ruarkings, 
but are quite irrespective of them.” 
Pecten Sowerbii was referred by Prof. M'CJoy in bis second de- 
scription of the shell 2 to tbe genus Amussium, a reference wbicb is 
considerably strengthened by the inequality wbicb must exist from 
tbe peculiar form of tbe ears in tbe two valves, and by tbe more or 
less circular or oval tiattened form. To complete tbe analogy we 
only require tbe interior radiating ribs, wbicb bave not yet come 
under my own observation in this species. There are also certain 
analogies witb tbe genus Pseud-amussinm, to wbicb it bas been referred 
by Prof, de Köninck, 8 but even more so witb the genus Entolium, 
Meek. I bave lately bad an opportunity, through the kindness of my 
friend Dr. Bigsby, F.R.S., of seeing Hayden’s Final Report on the 
U.S. Geological Survey of Nebraska, in wbicb Mr. Meek gives a 
description of Entolium ( Pecten ) aviculatum, Swallow. 4 Tbe 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 tbe group,” says Mr. Meek, “ is more 
than sub-generically distinct from Pseud-amussinm, Brug. It differs 
from Amussium mainly in baving no internal costse, and in having 
tbe valves more nearly equal, witb, sometimes, minute radiating 
striae, and no traces of a sinus under tbe anterior ear in either valve. 
The species known to me have tbe Cardinal margin of the left valve 
angulated in outline by tbe elevation of the extremity of the ears, 
wbile tbat of tbe right valve appears to be straight, and articulated 
in a little transverse groove of tbe otber valve, not always defined 
however The cartilage pit is as in otber allied types of the 
Pectinidae, wbile diverging from it are two otber tooth-like ridges. 
These, however, do not seem to bave been properly teeth, fitting 
into sockets, but appear to bave been a little raised in botb valves, 
and occupy a position between the ears and tbe broad diverging im- 
pressions, descending obliquely from tbe beaks.” 5 
Externally, E. aviculatum is almost identical with our P. Sowerbii, 
a fact wbicb bas not escaped tbe observation of Mr. Meek ; but I bave 
never as yet seen the above structure in tbe hinge of tbe latter, and 
therefore, for tbe present, I refrainfrom definitely referringP. Sowerbii 
to Entolium, as Mr. Meek bas done. 6 Tbe two forms certainly bear 
a very great resemblance to one anotbei - , even to the presence of 
tbe v-strice in Entolium. Mr. Meek assigned certain cbaracters on 
wbicb be based a specific distinction between the two forms, one 
being tbe presence of a number of “minute obscure radiating s tri je”; 
1 Annals Nat. Hist. 1876, vol. xviii. p. 424. 2 Brit. Pal. Foss. p. 478. 
3 Mon. Foss. Carb. Bleiberg en Carenthie, 1873, p. 94. 
* p. 189. 6 ibid. p. 190. 6 PI. xix. fig. 13. 
