34 Lamarck's Genera of Shells. 



times almost truncated. Ligament narrow, and so compact, 

 that the valves seem to be joined together on the hinge side» 

 and admit of httie motion for opening them. Textnre of the 

 shell, though thin and sometimes foliated, sohd ; its fracture 

 exhibits delicate transverse strife, similar to those of gypsum. 



The pinnoe are distinguished from the mytili, by the straight- 

 ness of the beaks, and the gaping of the superior extremity. 



The animal is long, without any projecting siphon, and has- 

 a conical linguiform foot, which it uses in fixing its fine, long, 

 shining, and silky byssus. 



Type. Pinna rudis * (Idem, TAnn.) 

 Shell large, oblong, ferruginous red ; apex oblirjuely rounded ; 

 furrows thick, sqnamiferous ; squamae large, semi-tubular. 

 Atlantic Ocean. IG Species. PI. I. Fig. 80. 



3rd Family. 

 Malleacea. (.3 Genera.) 



Ligament marginal, sulilincar, cither interrupted by indenta- 

 tions, or serial teeth, or quite simple. Shell sub-ineqnivalve, 

 foliated. 



Although allied to the mytilacea by similarity of position of 

 the ligament, the mallacea differ from them by the foliated tex- 

 ture of the shell, and by its being irregular and inequivalve. 

 Their ligament also is not perfectly internal, for, extending along 

 the lower margin of the valves, the facets which receive it in- 

 cline outwards, forming an open channel, and discovering more 

 or less of the ligament. 



1. Crenatula t. 



Shell subequivalve, flattened, foliated, rather irregular. No 

 particular aperture or pit for the byssus. Hinge lateral, mar- 

 ginal, linear, indented ; indentations serial, callous, hollowed 

 into pits, and receiving the ligament. 



The hinge of the crenatula a good deal resembles that of the 

 perna, but it is singular, by presenting a row of callous and rather 

 concave indentations, which receive the ligament, whereas that 



• Rude, t A littU notch, — dim. from crenu, the twtch of or, anow, kc. 



