240 SOLENID.'E. 



SOLEN, LiNN'.'EUs. 



Shell transversely greatly elongated, subcyllndrical, more 

 or less compressed, equivalve, inequilateral, gaping at both 

 extremities ; surface diagonally comparted, invested with 

 an epidermis. Muscular impressions distinctly marked, 

 dissimilar, the posteal oblong, the antcal greatly elongated ; 

 palleal impression with a wide, short sinus at its posterior 

 extremity. Hinge variable in structure and position, some- 

 times terminal, sometimes subcentral ; usually composed of 

 well-defined cardinal teeth and a lateral ligamental fulcrum 

 in each valve. Ligament external, elongated. Valves 

 beneath the hinge internally strengthened by a more or 

 less distinct and oblique rib. 



Animal very narrow, more or less cylindrical or com- 

 pressed; mantle united at the borders, except anteriorly, 

 where it opens for the passage of a large, long, thick, 

 oblique, truncated foot. Siphons short, united, their ori- 

 fices fimbriated. Branchiro prolonged into the inferior 

 siphon. Labial palpi long, narrow, and triangular. 



Aristotle, in his " History of Animals," mentions more 

 than once a shell-fish under the name of ao)\r]v, in such 

 expressive terms that we can scarcely doubt its identity 

 with the razor-fish, in all probability the first of the 

 species to be hereafter described. He states that it buries 

 itself in sand, perpendicularly, even to a depth of two 

 feet, and can rise and sink in, but does not leave its hole ; 

 that it does not spin a byssus wherewith to fix itself, like 

 other testacea ; that it is alarmed by noise, and buries 

 itself rapidly when frightened ; that the valves of the shell 

 are connected together at both sides, and tliat their surface 

 is smooth. Such an enumeration of character indicates 



