32 Mr. R. Etheridge on Carboniferous Mollusca. 



I have on previous occasions fully described E. Sowerhii ; 

 and it now only remains for me to refer to its relation with E. 

 aviculatum. The close resemblance of the species was recog- 

 nized and commented on by Mr. Meek himself ; and the only 

 points which he was able to use as distinctive characters were, 

 the stronger concentric markings, absence of obscure minute 

 radiating strise, and the more pointed and elevated ears of E. 

 Sowerhii. The strength of the concentric laminee is a cha- 

 racter which entirely depends upon the state of preservation 

 of the specimen examined ; in some individuals the lines are 

 strong and well marked, in others scarcely perceptible. I 

 have already shown "^ that E. Sowerhii does possess " obscure 

 radiating strise," which were particularly well shown in a speci- 

 men lent me by Mr. A. Patton. With regard to the acute- 

 ness and elevation of the ears, as little reliance can be placed 

 on this as on the concentric strije ; for their general appearance 

 does, to some extent, depend upon the position in which the 

 shell was deposited previous to fossilization. I think there 

 can be no better proof of their probable, if not absolute, iden- 

 tity than the fact, that so close and accurate an observer as 

 Mr. Meek was unable to point out any more stable points of 

 difference than the above. In conclusion, it may be stated, 

 therefore, that in both forms the shell was thin and probably 

 fragile, ornamented with concentric stria of greater or less 

 degree of strength, supplemented by fine radiating lines, and, 

 under certain conditions, exhibitiug the characteristic V-shaped 

 markings or grooves over the whole shell ; and, lastly, the 

 hinge-structure is identical. It is always the wiser course, in 

 dealing with specimens one has not personally examined, to 

 speak with caution and a certain amount of reserve ; but I 

 am under the impression that E. aviculatum, Swallow, can at 

 the best be only retained as a variety oi E. Sowerhii^ M'Coy. 



The following species have the outward appearance of the 

 genus Entolium (and it will be well for those possessing speci- 

 mens, or access to such, to endeavour to elucidate the hinge 

 and general internal structure of the shells) , viz. : — 



1. Pecten discites (Schl.), Goldfuss, Pet. Germ. ii. t. 98. 



f. 10, d. 



2. P. cingulatus (Phill.), id. ibid. t. 99. f. 3, h. 



3. P. laminosus (Mantell), id. ibid. t. 99. f. 9. 



4. P. striolatus, Goldfuss, Pet. Germ. ii. t. 160. f. 7. 



5. P. Phillipsii, id. ibid. t. 160. f. 6. 



P. cristatusy Bronn, as figured by Goldfuss {loc. cit. t. 99. 

 * Geol. Mag. dec. 2, iv. p. 242. 



