206 BULLETIN OF THE 
MOLLUSCA VERA. 
Ciass PELECYPODA GoLpFuss. 
Famity PECTINIDA. 
Genus PECTEN Mutter. 
Pecten Miiller, Prodr. Zool. Dan., p. xxxi, 1776. Type Pecten (Ostrea) mazi- 
mus L., 1. c., p. 248. 
This ancient genus has been cut up into many sections, most of which shade 
into one another by imperceptible gradations, or interchange characters, or 
would belong to different sections at different stages of post-embryonic growth. 
For purposes of convenience and usefulness most of these sections were better 
discarded, as a name without any essential characters is merely an incumbrance 
to workers and a stumbling-block for learners. For my own purposes I find 
the following arrangement convenient : 1. Pecten, with the subgenera Janira ; 
Amusium and section Propeamusium ; Pseudamusium and section Camptonectes ; 
Pecten typical and the sections Palliwm and Lyropecten ; 2. Netthea ; 3. Hemi- 
pecten; 4. Hinnites. 
In form of shell and characters of hinge, Dimya is related to Pecten, and by 
its habit to Hinnites ; in its shell structure, it is nearer the Aviculide@ and 
Ostreide ; in its anatomical peculiarities it is archaic, foreshadowing the pearl- 
shells, the oysters, and the scallops in different degrees. It is well entitled to 
family rank, and for present purposes I prefer to arrange it between the Pecti- 
mide and the Aviculide, though no linear arrangement will express all its 
relations. 
The form of the foot in typical Pecten is recorded as cylindrical, with or with- 
out the posterior margin grooved. In P. cawrinus the groove is deep, the stem 
calibre uniform, the distal end a little swollen, with a minute slit and radiated 
aperture on the posterior median line, the whole extremely phallic in appear- 
ance ; in P. antillarum the foot is grooved, subcylindrical and worm-like, with 
no perceptible slit at the tip, and that of P. nucleus Born is much the same ; 
P. irradians has a beginning of a sucker-slit and hardly expanded tip ; P. ma- 
gellanicus has the tip much enlarged, solid, with a large sucker ; when we get 
to Amusiwm pleuronectes we have a spade-shaped tip and well-developed sucker, 
with moderate stem ; and, finally, in A. Dall the sucker is large, hood-shaped, 
thin-walled and darkly pigmented, with a broad base abruptly enlarged from 
a very slender stem. Similar modifications appear in the anal extremity, 
which from elongate and free varies to the usual appressed type of most bi- 
