PECTEN. 49 



The foot emits a powerful coarse byssus, which cannot be 

 detached without laceration of the body, but the strands are 

 easily separated from the substances on which they are fixed ; 

 this is contrary to the usual plan of the Bivalves, which, when 

 a change of locality takes place, is effected by drawing the 

 byssus from that part of the foot-groove close to the body, 

 and leaving it moored to the substance on which it was fixed : 

 this operation we have witnessed even in confinement. This 

 species is given as an example of the variation of specialties ; 

 all the others afford nearly as decided ones. 



I trust that some northern observers will compare the P. 

 tigrinus, P. striatus and P. furtivus, all of which we believe 

 are identical, and communicate the result: if they are distinct, 

 malacologists will have no difficulty in seizing the distinctive 

 characters. Speaking conchologically, we should say that the 

 three so-called species are only variations of the old P. obso- 

 letus of authors, now styled P. tigrinus. 



This species is either free, or adheres by the byssus to 

 marine substances, but is not imbedded in them by the under 

 valve, as in the P. pusio. 



P. PUSIO, Pennant. 



P. pusio, Brit. Moll. ii. p. 278, pi. 50. f. 4, 5, and pi. 51. f. 7- 



P. distortus, Montagu. 



P. sinuosus, Turton et Auct. 



The body and ovaiy throughout are either intense vermi- 

 lion, or of a uniform pale yellow-white, and not half white 

 and half vermilion, as in P. opercularis ; at least in P. pusio 

 we have never observed this to be the case. The branchiae 

 are dull red-brown, and the palpi pale brown ; there are two 

 connecting rows of pale red cirrhous fringe around the mouth. 

 The back or free margin of the reflected mantle has two to 

 three rows of irregular, short, yellow- white, blunt filaments. 

 The ocelli are larger, fewer, and more distant than in the 

 type. The fixed or anterior marginal circle has a row of 

 large, long, conical, pointed, yellow filaments, and in front 

 of it two to three irregular rows of shorter cirrhi of different 



E 



