Pvn H,i I'UitlS

254 LUCINID.E.
Diplodonta rotunda'ta*, Montagu.
Tellina rotundata, Mont. Test. Brit. p. 71, tab. 2. f. 3. D. rotundata,
F. & H. ii. p. 66, pi. xxxv. f. 6, and (animal) pi. M. f. 7.
Body clear white :
gills laminar, somewhat elongated and
angular, folded or puckered at the edges, pectinated, and fixed
as usual to the dorsal range, the upper plate being little more
than half the depth of the lower one : palps short, pointed,
pectinated, and somewhat triangular :
end very small and : inconspicuous foot central, rather long,
and conical, minutely perforated at the point.
orifice at the posterior
Shell obliquely quadrilateral, gibbous, not very thin, opaque,
moderately glossy: sculpture, strongly marked and irregular
lines of growth, and (under the microscope) exceedingly fine
and close-set, regular longitudinal lines on the umbonal area,
which radiate from the beak and are only perceptible in fresh
specimens, as well as equally fine and numerous, but irre-
gular and often wavy or confluent, transverse lines on the
rest of the surface : colour milk-white : epidermis
fibrous and
yellowish, usually rubbed off except in front : margins obtusely
angular on the anterior side, where the slope to the beak and
front is nearly equal, obliquely rounded in front, somewhat
produced and very much broader on the posterior side, which
is also rounded at the end, and straight behind : beaks small,
scarcely projecting beyond the dorsal line, and not contiguous :
lunule very small, but deep, not well defined, and hidden by the
beaks : ligament short, semicylindrical, yellowish-brown
or of
a golden hue, projecting beyond the dorsal margin ; ligamental
groove rather deeply cut : hinge-line slightly curved, occupying
nearly one-third of the circumference : hinge-plate broad
in the middle and tapering gradually to each end the ; posterior
side is the longer: teeth, in the right valve two erect
cardinals, the posterior of which is double and placed more
lateral on each
obliquely than the other, as well as a plate-like
side, the anterior of which is distinct ; in the left valve the
same number and kind of cardinals and laterals, but the posi-
tion of the former is reversed : inside marked by slight longitudinal
lines, frost-like in the centre and at the back, but
glossy towards the margin, which is plain : pallial scar distinct,
broad, and entire : muscular scars large and well marked, the
anterior one irregularly elliptical, and the posterior oval.
L. 0-9. B. 1.
* Rounded.