106 MACTEID^l. 



triangular; in others, compressed, sharp at the sides, and 

 transversely produced, which variations have caused even the 

 excellent Montagu to err in the creation of his M. truncata 

 from one or other of the varieties of the M. solida or of the 

 M. subtruncata. Without being positively certain, we think 

 the M . truncata of authors must be expunged as a species ; 

 and whether it be a synonym of the M. solida or M. sub- 

 truncata is doubtful; at any rate, all the shells that have 

 been as yet shown us are referable to one or other of these 

 species. 



The contour of the M . solida, which is taken abundantly at 

 Exmouth at low water, in the sandy ranges adjoining the 

 Mare rocks, is of the tumid and subtriangular variety : it is 

 from this locality that Dr. Turton obtained the types of his 

 M. crassa. 



M. ELLIPTICA, Brown. 

 M. elliptica, Brit. Moll. i. p. 356, pi. 22. f. 3 ; (animal) pi. L. f. 1. 



Animal suboval, compressed ; body flake-white ; liver green, 

 scarcely visible, being covered by the opake white tough dorsal 

 skin ; mantle open, very slightly fringed anteally, plain pos- 

 teally ; siphonal tubes in a specimen f of an inch transverse 

 by | an inch vertical measure, are not exserted more than 

 |ths of an inch, and appear as if enveloped in a sheath; each 

 orifice has about twelve cirrhi at their bases, below which 

 a bright orange line encircles the sheath, which is of pale 

 yellow. The branchiae are light orange, subsemicircular, the 

 upper being much smaller than the lower, and very finely 

 pectinated. The palpi are long, narrow, pointed, pale brown, 

 and more conspicuously striated than the laminae. Foot 

 white, rather large, muscular and lanceolate, by the aid of 

 which the animal turns its shell, with great ease, from side 

 to side. 



This species appears distinct, and though it is difficult to 

 define distinctions by the organs, which in all the Mactrae. are 

 so similar, still there is a delicacy and elegance in the appear- 

 ance of this creature which almost assures us that it is not a 

 dwarfish variety of the M. solida, which at Exmouth is strictly a 



