12 GENERA OF SHELLS. 



very slight. Hinge linear, marginal, without 

 teeth. 



G. cuneiformis, mytiloides, modioJina. 



SOLENACEA. 



Shell loithout accessory pieces, and gaping only at the lateral 

 extremities ; ligament external. 

 The solenacea bury themselves m the sand, but do 

 not perforate wood or stone. 



SoLEN. Shell bivalve, equivalve, elongated 

 transversely, gaping at both ends, with small, 

 inconspicuous beaks ; cardinal teeth small, va- 

 riable in number, sometimes wanting, rarely 

 diverging, more rarely received into grooves ; 

 ligament external. 



S. vagina, corneus, vaginoides, siliqua, ensis, pygmaeus, 

 ambiguus, cultellus, planus, minutus, legumen, Dombeii, 

 Javanicus, Caribaeus, antiquatus, constrictus, coarctatus, stri- 

 gilalLis, radiatus, violaceus, rostratus, — costatus, centralis, 

 viridis. 



Panoptea. Shell equivalve, transverse, une- 

 qually gaping at the sides, a conic, cardinal 

 tooth on each valve, and a compressed, short, 

 ascending callosity by its side, not projecting 

 outwards ; ligament exterior, on the longer 

 side, fixed to the callosities. 



The Panopaea differs from the glycimeris, by having 

 cardinal teeth, and by the ligament being on the long- 

 est side ; from the solen by the greater projection of 

 the beaks, and from mya by the ligament being ex- 

 tenial. 



P. aldrovandi. 



