Pvn H,i I'UitlS

SCROBICULARIA. 435
A. Lateral teeth more or less developed.
1. Scrobicularia prisma'tica *, Montagu.
Ligv.la prismatica, Mont. Test. Brit. Suppl. p. 23, t. 26. f. 3. Syndosmyu
prismatica, F. & H. i. p. 321, pi.
xvii. f. 15.
Body pearl-white : mantle fringed with short and numerous
cilia : tubes cylindrical and slender, indistinctly annular or
corrugated by the investing sheaths ; they are nearly of the
same length, the incurrent being the larger or wider but
excurrent or upper tube stran-
usually the shorter of the two ;
gulated or constricted at irregular intervals ; both tubes are
clothed with a few scattered papillae, and the orifice of each
has from 5 to 7 short cirral points, which are sometimes obso-
lete or imperceptible: gills two on each side, suboval, of equal
tinted with brown
: size, distinctly pectinated, faintly
the same in number, thin, short, broad, and angular, smooth
without and striated within :
foot large and pointed.
Shell oblong and wedge-shaped, scarcely convex, but not
palps
flattened except towards the posterior end, very thin and fra-
gile, semitransparent, highly polished and glossy: sculpture,
numerous slight, irregular, and minute concentric striae, which
occasionally are laminar or scratch-like, and towards the mar-
gins become partially oblique, as in Tellina fabula ; the lines
of growth are also more or less conspicuous : colour pearlwhite
: epidermis a mere film, reflecting in certain lights a prismatic
lustre : margins curved in front, semioval or rounded on
the anterior side, and bluntly pointed on the posterior side,
which is flexuous and obtusely angulated; dorsal margin nearly
straight on the anterior side, incurved below the beak, sloping
outwards from the posterior angle, and obliquely truncate on
that side, the point or terminal angle lying in the transverse
axis of the shell : beaks very small ; umbones somewhat pro-
jecting: ligament short, prominent, yellowish-brown: cartilage
curved, horncolour, proceeding from a narrow chink under
the beak, and expanding in a shelving and oblique direction
below the hinge-plate on the posterior side : hinge-line obtusely
angular and flexuous: hinge-plate rather thick, much
broader and reflected behind the cartilage : teeth, in the right
valve two minute, erect, equal- sized, parallel, and obliquely
set cardinals, besides a long but slight lateral on each side,
* Having a prismatic lustre.