Mr. R. Etheridge on Carboniferous Mollusca. 31 



P. Sowerlii was previously unknown to me, although, from 

 the great resemblance between the foregoing species, I felt 

 convinced that time only was necessary to prove, at least to 

 some extent, Mr. Meek's supposition. By the fortunate dis- 

 covery of some well-preserved casts of P. Sowerhuj by Mr. J. 

 Bennie, at Teasses Quarry, Fife, I am now able to demonstrate 

 the fact that the latter is a species of Meek's genus Entolium, 

 and that there is very little if any difference between E. avi- 

 culatunij Swallow, and E. [Pecten) Soiverbu\ M'Coy. 



For comparison I have given figures representing the hinge 

 of the Oolitic form, E. demissum, PhilL, and the Carboni- 

 ferous E. aviculatum, Sw., after Quenstedt * and Meek t re- 

 spectively. 



If we first examine the cast of the valve of E. Soiverhii 

 (fig. 4) with ears, we observe a small projection at a, which 

 is the mould of the cartilage-pit, and corresponds with a 

 similar pit in E. demtssum (fig. 1) and E. aviculatum (fig, 2). 

 Extending from this are two transverse ridges, one on 

 each side {h, b), which are the moulds of the transverse 

 furrows seen in the other species (figs. 1, 2). Extending ob- 

 liquely from the cartilage-pit are two deep furrows (c, c), the 

 moulds of two large diverging teeth strongly marked in relief 

 in the interior of ^. demtssum (c, c, fig. 1) and E. aviculatum 

 (c, c, fig. 2). From the distal extremities of these extend two 

 longer but shallower furrows (c?, d)^ also represented in the 

 other specimens as ridges (c7, «?, figs, 1, 2). It is to be re- 

 marked that in by far the larger number of specimens of E. 

 Sowerbii collected from our Carboniferous rocks the ridges 

 (d,^ d) are visible externally, and have been referred to in de- 

 scriptions of this species by Prof. M'Coy and myself. The 

 posterior is usually the longer of the two. 



In the opposite valve, that with the flat or normal ears 

 (fig. 5), we see no trace of the transverse furrows (Z», b)^ but 

 still the oblique ones (c, c), identical with ridges in the corre- 

 sponding valve of E. aviculat^im (c, c, fig. 3) ; there are also 

 present the extended ridges (d^d, fig. 5). 



Of the diverging ridges (c, c) Mr. Meek remarked, " 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 tlie broad diverg- 

 ing impressions {d,d), descending obliquely from the beaks." 

 The transverse grooves {b,b in figs. 1,2, and 4) were re- 

 garded by Mr. Meek as a receptacle for the articulation of 

 the straight cardinal margin of the opposite valve (figs, 3, 5). 



* Der Jura, Atlas, t. 48. f. 6. 



t Haydeu's Final Report on Nebraska, t. 9. f. 11,/, ff. 



