106 MACTRID. 
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 1s 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 adjoming the 
Mare rocks, is of the tumid and subtriangular variety: it 1s 
from this locality that Dr. Turton obtained the types of his 
M. crassa. 
M. evurptica, Brown. 
M. elliptica, Brit. Moll. 1. p. 356, pl. 22. f. 3; (animal) pl. L. f. 1. 
Animal suboval, compressed ; body flake-white ; liver green, 
scarcely visible, bemg covered by the opake white tough dorsal 
skin; mantle open, very slightly frmged anteally, plain pos- 
teally ; siphonal tubes in a specimen # of an inch transverse 
by $ an inch vertical measure, are not exserted more than 
éths 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 branchiz are light orange, subsemicircular, the 
upper being much smaller than the lower, and very finely 
pectmated. The palpi are long, narrow, pointed, pale brown, 
and more conspicuously striated than the lamime. 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 Mactre 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 
