72 CARBONIFEROUS LAMELLIBRANCHIATA. 



which describes A. coelatus, M'Coy. I suppose that by a concave left or upper valve 

 Fleming was either thinking of the interior, or had a crushed specimen, as I know 

 of no Carboniferous Pectiniform shell with a valve concave externally. Phillips 

 figured both valves of what he took to be Pecteit dissimilis, one of which, the right 

 valve, is preserved in the Gilbertson Collection of the Natural History Museum, 

 South Kensington. This shell (PI. XIII, fig. 5) has the peculiar marking of the 

 right valve beautifully preserved, though unfortunately much of the ears has been 

 broken off. Whether or no the specimen figured as the left valve belongs to the 

 same species is doubtful, and Phillips placed a query before it. The specimen 

 having disappeared, it is now impossible to say more about this point. 



There can be no doubt that the shell described by M'Coy as A. coelatus is 

 the left valve of Fleming's species, for several specimens of bivalved examples 

 from Beith, Ayrshire, in the collection of Mr. J. Neilson, of Glasgow, demonstrate 

 the fact that the left valve of A. coelatus, M'Coy, and the right valve of Pecten 

 dissimilis, Fleming, are one and the same species. It is to be noted that A. coelatus, 

 M'Coy, was founded on a left valve, and that author makes no mention of the right 

 valve. It is also noteworthy that M'Coy, referring to P. dissimilis, considers that 

 Fleming's and Phillips's shells were not the same. There can be little or no doubt 

 that A. textilis, cle Koninck, is the right valve of A. dissimilis, although the former 

 is from the Tournai beds and the latter from Vise. The shape and ornament 

 of the ears, and the ornament of the body of the shell, are identical with what we 

 know to be the right valve of A. dissimilis. 



P. arenosus agrees with A. dissimilis in the character of the ornament of the 

 two valves. The ribs of the former are more numerous, closer, and finer, and the 

 concentric ribs of the right valve comparatively fewer and broader than in the 

 latter. It is possible that the one may only be a juvenile condition of the other. 



Mr. R. Etheridge recognised the peculiar character of the right valve, but 

 retained the name A. coelatus. 



I consider that /'. subfimbriatus, de Verneuil, should be referred to A. dissimilis, 

 likewise the shell referred by Portlock to P. ottonis. In both of these cases the 

 left valves only were figured or described. 



Pecten concentrico-striatus, M'Coy, evidently, and P. undulatus probably, are the 

 right valves of A. dissimilis. The latter has the posterior ear broken, which there- 

 fore appears too short. I also believe P. rugulosus to represent a left valve. 

 All three types arc in the Science and Art Museum, Dublin. 



The type of Pecten arenosus, Phillips, has unfortunately disappeared, and I 

 think it probable that it may have been the right valve of a young specimen of 

 A. dissimilis, because the meagre description reads — " Radiating strise very 

 u ii i iierous, alternately larger ; minutely crenulated with many sharp circular stria?." 

 It is true that " rather short square ears " hardly agree with A. dissimilis, but it is 



