NATURAL SCIENCES OF PHILADELPHIA. 125 



adopted for the specific description, (see the paper referred to.) The latter 

 may constitute the type of still another species. 



The species described as Avicula Whiter, Win., and Gervillia strigosa, 

 White and Whitfield, should probably be referred to Pterinea in accordance 

 with views recently put forth by Mr. Meek. 



Aviculopecten Caroli, Win. This species first described from the yellow 

 sandstone at Burlington, Iowa, is found also in the base of the Burlington 

 limestone at the same locality. "White Collection." 



Aviculopecten texuicostus, Win. A very small specimen, collected by A. 

 Winchell, at Rockford, Indiana, seems to agree with the above Burlington 

 species. 



Other specimens collected at Germain's quarry, Hillsdale, Michigan, have 

 the same proportions and general surface characters, but they are once and a 

 half as large as the Burlington types, and the anterior auriculation is marked 

 by coarser, instead of finer striae. The body of the shell presents about 57 

 striae and the anterior ear 8. 



The foreign analogue of this species seems to be Pecten arenosus, Phillips. 



PERNOPECTEN, new genus. 



Etymology. Perna and Pecten, from a combination of some of the charac- 

 ters of the two genera. 



Generic Characters. Shell bivalve, sub-equivalve, monomyary. Valves 

 more or less inequilateral and auriculate. Hinge line straight ; hinge fur- 

 nished with a central, triangular cartilage pit, and a transverse plate bearing 

 on each side of the middle a series of smaller pits diminishing in size and 

 depth from the centre outwards. The shell seems to be thin, and probably 

 has a structure more like Pecten than Perna. 



This genus, or subgenus is founded on Aviculopecten linueformis, White and, 

 Whitfield, (Proc. Bos. Soc. Nat. Hist. vol. viii. p. 295.) My attention was. 

 first directed to the peculiarity of the hinge structure in two or three speci- 

 mens sent me by Dr. White himself; and an examination of a number of spe- 

 cimens previously referred to this species shows that they all possess it. The- 

 genus Aviculopecten, happily constituted by McCoy to receive a number of 

 paleozoic species having affinities with Pecten in their external form, and with. 

 Avicula in their cardinal structure, is made by its author to differ from Pecten 

 by the absence of a central ligameutary pit, and from Avicula by its nearly 

 equilateral outline. The present genus differs from Avicula and Aviculopec- 

 ten, and approaches Pecten and Monatis, in the presence of a mesial ligament- 

 ary pit ; and it ditfers equally from Pecten, Aviculopecten and Avicula, and ap- 

 proaches Perna, by the presence of a series of isolated ligameutary pits in the 

 cardinal area. It differs from Perna in its sub-central beaks, with ligamentary 

 pits on both sides. It agrees with Amusium in its sub-symmetrical ears, cen- 

 tral cartilage pit, and the absence of radiating ridges, but differs in its straight 

 hinge line and lateral cartilage pits. The position of the genus i* apparently 

 between Perna and Pecten, with a preponderance of affinities for the latter, 

 sufficient, perhaps, to throw it into the family of Pectinidw, White. Aviculo- 

 pecten is grouped with the Aviculida. 



It is probable that in addition to the two following species,, others referred i 

 to Avicula, Pterinea, and more especially Aviculopecten, Amusium, and Pecten, 

 will be found to possess the assemblage of characters shown in Pemopecten 

 Lima ? obsoleta, Hall, (Rep. 10th Dist. N. Y., p. 265,) = Pecten. subobsoletus, 

 d'Orb., is stated to have a " crenulated hinge line," while its external char- 

 acters are quite conformable to Pemopecten. Not improbably Lima glaber, 

 Hall, belongs in the same association. The same may be said of, Pecten den- 

 sistria, Sandb., from the Posidonomyenschie/er of Nassau ;- Avicula, tumida and. 



1865.] 9 



