206 BULLETIN OF THE 



MOLLUSCA VERA. 



Class PELECYPODA Goldfuss. 



Family PECTINID^. 



Genus PECTEN Mulleb. 



Pecten Miiller, Prodr. ZooL Dan., p. xxxi, 1776. Type Pecten {Ostrea) maxi' 



mus L., L c, p. 248. 



This ancient genus has been cut wp 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 Camptonedes ; 

 Pecten typical and the sections Pallium and Lyropecten ; 2. Neithea ; 3. Hemi- 

 pecten; 4. Ilinnites, 



In form of shell and characters of hinge, Dimya is related to Pecten, and by 

 its habit to Ilinnites ; in its shell structure, it is nearer the Aviculidoe and 

 Ostreidos ; 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- 

 nidce and the Aviculidoe, 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. caurinus 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 Amusium pleuronectes we have a spade-shaped tip and well-developed sucker, 

 with moderate stem ; and, finally, in A. Dalli 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- 



