52 PECTINIM. 



pitted, and sometimes very finely and closely striate length- 

 wise: muscular scars slight. L. 1*65. B. 1-45. 



HABITAT : Every rocky coast from Shetland to Corn- 

 wall, often on oyster-beds, and attached in the adult 

 state by the whole or last-formed part of its lower valve 

 to the inside of old bivalve shells, or to rocks, Eschara 

 foliacea, and other substances. The depth of water in 

 which it lives varies from 5 to 85 fathoms, and the 

 young are occasionally found at low- water mark on 

 some shores where the tide retires for two or three 

 fathoms. In a fossil state P. pusio occurs in the Clyde 

 beds, as well as in the Red and Coralline Crag. Its 

 extra-British range is considerable, extending from Nor- 

 way to the Azores on the one side and to the .^Egean on 

 the other. 



In more northern seas this species soon fixes itself 

 permanently to various bodies by means of an aggluti- 

 nating secretion ; but in the Mediterranean and more 

 southern latitudes it usually remains free, or attached 

 by a byssus only, from which it has the power of 

 withdrawing or disengaging itself at pleasure. In the 

 former or fixed state it belongs to the genus Hinnites 

 of Defrance. It has been clearly shown, however, by 

 the late Mr. G. B. Sowerby thirty-five years ago, on con- 

 chological grounds, and by Dr. Fischer in 1862, physio- 

 logically, that this species is a true Pecten, and that the 

 genus Hinnites is not maintainable. The peculiar mode 

 of attachment by the shell in this case is the reverse of 

 that adopted by the oyster, the former having the 

 smaller valve and the latter the larger valve uppermost. 

 The prickly scales are sometimes produced also on the 

 lower valve, and become leaf-like or foliated as in the 

 oyster. In fixed specimens the byssal sinus is more 

 or less closed; but I have some of a large size and 



