NATURAL SCIENCES OF PHILADELPHIA. 
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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 Whitei, Win., and Gervillia strigosa, 
White and Whitfield, should probably be referred to Pterinea in accordance 
with views recently put forth by Mr. Meek. 
Aviculopecten Caeoli, 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 tenuicostus, 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-equi valve, 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 limceformis , 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 ligamentary pit, and from Avicula by its nearly 
equilateral outline. The present genus differs from Avicula and Aviculopec¬ 
ten, and approaches Pecten and Monotis, in the presence of a mesial ligament¬ 
ary pit; and it differs equally from Pecten, Aviculopecten and Avicula, and ap¬ 
proaches Perna, by the presence of a series of isolated ligamentary 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 is apparently 
between Perna and Pecten, with a preponderance of affinities for the latter, 
sufficient, perhaps, to throw it into the family of Pectinidce, While. Aviculo¬ 
pecten is grouped with the Aviculidce. * 
It is probable that in addition to the two following species, others referred 
to Avicula, Pterinea, and more especially Aviculopecten, Amusium and Pecten, 
will be found to possess the assemblage of characters shown in Pernopecten 
Lima ? ohsoleta, 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 Pernopecten. Not improbably Lima glaber, 
Hall, belongs in the same association. The same may be said of Pecten den- 
sistria, Sandb., from the Posidonomyenschiefer of Nassau : Avicula tumida and 
1865 .] 9 
