166 MYAD^. 



tooth, which, scarcely elevated above the hinge-marghi, 

 lies ill front of the cartilage-pit, which latter shelves clown 

 almost at right-angles to the dorsal line. 



The proportion of length to breadth is not constant ; 

 specimens which are two inches wide, measuring from three 

 and a quarter down to two and a half inches only between 

 their lateral extremities. 



The animal is oval with very long siphons, the epider- 

 mic coat, which invests the mantle and tubes, is rugose and 

 brown ; beneath it the surface is white, or tinged with 

 yellow, so also is the foot. The viscera are of a pale 

 brown hue. The mantle is entirely closed in front except 

 a small aperture anteriorly for the narrow linguiform foot, 

 w^hicli is straight, and furnished with a byssal groove. The 

 suture of the united margins of the mantle is conspicuously 

 seen when the investing coat is removed. That part of the 

 sheath which surrounds the siphons is marked dorsally and 

 ventrally by a ridge or suture. The siphonal tubes are 

 united to their extremities, or very nearly so. They are 

 both surrounded at the point of separation by a circle of 

 filaments, the bases of which are tinged with brown. The 

 branchial orifice is especially fimbriated. A tubular mem- 

 brane is protruded from the interior of the anal orifice. 

 The branchia; are partly continued into the tube. The 

 labial tentacles are large, triangular, acute, and striated 

 upon their inner sides. 



In Zetland, this animal is boiled and eaten. It is there 

 called " Smurslin." The species is abundant on the coast 

 of Newfoundland, where it is said to be a favourite food of 

 the cod-fish. 



Our association of Sphoenia Swainsoni and Mya ovalis 

 with the present species, results from a careful examination 

 of Turton's original types, which are still preserved and in 



