Pvn H,i I'UitlS

MACTRA. 41 7
or less glossy, microscopically freckled, often iridescent, and
slightly streaked lengthwise towards the front margin : pdllial
scar distinct, with a short and tongne-shaped sinns : muscular
scars irregularly triangular, deep, and of equal size. L. 1*4.
B. 1-6.
Var. 1. truncata. Shell longer in proportion to its breadth,
sides more compressed or
gibbous, and of a thicker texture ;
truncate ; umbones prominent; hinge and teeth stronger. M.
truncata, Montagu, Test. Brit. Suppl. p. 34 ; F. & H. i. p. 354.
pi.
xxiii. f. 1.
Var. 2. conjunctiva. Shell much smaller, having
the same
proportions as the variety truncata, and also rather ventricose,
but thin ; umbones not more prominent than usual. L. 0*6.
B. 0-85.
Var. 3. elliptica. Shell invariably smaller than the typical
form, broader in proportion to its length in consequence of the
sides being more produced, and of a thinner texture umbones
;
not prominent. L. 0*75. B. 1-25. M. elliptica, Brown, 111.
Conch. G. B. & I. p. 108, pi.
xli. f. 6 ; F. & H. i. p. 356, pi. xxii.
f. 3, and (animal) pi. L. f. 1.
Habitat : In gravelly sand, at low tides and at the
depth usually of only a few fathoms, on every coast.
Var. 1. South of Devon and Cornwall, Tenby, Irish
coasts, Firth of Forth, Clyde district, Orkneys, and
Lerwick. Var. 2. Shetland (J. G-. J.). Var. 3. Sandy
of from 10 to 100 fathoms : the dorsal
bays, at depths
area is sometimes ribbed in the variety elliptica, as well
as in the typical form. This exceedingly variable spe-
cies occurs in all our newer tertiaries, from the last
raised beach to the Coralline Crag. The ordinary kind
and the variety truncata have been chiefly noticed as
littoral and in southern latitudes, their furthest limit
being Sicily, where the former is also fossil ; the only
northern locality that appears to be recorded is the
Scandinavian coast, on the authoritv of O. F. Mul-
ler. The variety elliptica has essentially a northern
range, from Iceland (Steenstrup)
to Kullen in the
t 5