Pvn H,i I'UitlS

312 CYPRINID.E.
cardinals, of which the middle one is by far the largest, trian-
gular, and blunt ; the other two are laminar and diverge in
opposite directions, the anterior tooth being the slightest ;
lateral teeth as in the right valve : inside chalky-white, with a
thin superficial layer which is microscopically tubercular and
glistening ; margin thickened in front and at the sides, and
finely crenulated or notched : pallia! scar narrow, slightly im-
pressed: muscular scars irregularly elliptical or conchoidal,
very distinct. L. 1*1. B. 1*2.
Yar. 1. paucicostata. Shell smaller, having fewer and
thicker ribs ;
inside margin either smooth or notched.
Yar. 2. Scotica. Shell usually rather compressed ; inside
margin thin and smooth. Venus Scotica, Maton and Rackett,
in Linn. Trans, viii. p. 81, t. 2. f. 3.
Yar. 3. elliptica. Shell commonly still more compressed,
broader than long, in consequence of the posterior side being
more produced than in the typical form ; upper or dorsal slope
nearly straight ; ribs more or less evanescent in front and at
the sides ; inner margin smooth. Crassina ellvptica, Brown,
111. Rec. Conch, p. 96, pi. xxxviii. f. 3. A. elliptica,
i. p. 459, pi. xxx. f. 8.
F. & H.
Yar. 4. truncata. Shell more than ordinarily triangular ;
front margin nearly straight
or truncate.
Yar. 5. minor. Shell smaller and more convex.
Yar. 6. trigona. Shell nearly as small as the last and de-
cidedly triangular.
Yar. 7. incrassata. Shell obliquely triangular ; ribs more
or less evanescent in front and at the sides. Venus incrassata,
Brocchi, Conch. Foss. Subap. ii. p. 557, tav. xiv. f. 7.
Yar. 8. multicostata. Shell somewhat triangular ; ribs numerous.
Habitat :
Sand
and mud, in 7-85 fathoms, on all our
coasts from Falmouth (Couch) to the Shetland Isles.
Captain Beechey dredged
it in 145 fathoms off the Mull
of Galloway. It is most plentiful in the west of Scot-
land. Mr. Jordan has lately taken numbers of it in
Milford Haven ; but otherwise it does not seem to be
common in the south. A. sulcata occurs in many of the