CONCHIFERA. 



279 



entire. Animal oblong ; mantle freely open, simple or 

 fringed; no siphons; foot large, oblong, bent, grooved 

 throughout its entire length so as to form a disk, with 

 plain or slightly crimped margins ; a byssal gland at its 

 base ; byssus compact ; mouth surrounded by labia formed 

 out of the extremities of the branchiae ; no true palpi.* — 

 122 species f ; also fossil. 



Some of the species live in holes, or bury themselves in 

 the sand, and others moor themselves by a byssus to stones, 

 coral, and rocks; a few have one valve larger than the 

 other, and many have a velvety or testaceous epidermis, 

 frequently ending in a deep fringe at the margin. They 

 are found in the Atlantic, Pacific, and Indian Oceans, and 

 the Mediterranean. Macgillivray says, that on the coast 

 of Australia, near Brisbane Water, he saw enormous 

 accumulations of dead shells of A. trepezizia, which at 

 first sight may be mistaken for raised beaches, these heaps 

 being often twenty feet or more in depth, and several 

 hundred yards in length, covered with a stratum of earth, 

 and large trees growing on them. The shells had for 

 ages constituted the principal food of the natives, who 

 were formerly very numerous."! The Area Noce, or 

 Noah's Ark, and several other species like it, in form and 

 character, are well known to the collector ; they are 

 amongst the most striking of the genus. Also A. tor- 

 tuosa and semitorta, which, as their names denote, are 

 curiously twisted. Two or three small species are found 

 on our coasts. 



Byssoarca of Swainson, is a sub-genus. 



Cucull^ea. Lam. — Shell equivalve, inequilateral ; 

 bosses not touching each other ; muscular impression 



* Forbes's British Moll. f Reeve's Iconica. 



% Voyage of the " Rattlesnake." 



T 4 



