Pvn H,i I'UitlS

LEPTON. 199
with an ordinary lens : colour varying from pale yellowish to
clear white : epidermis slight, bnt brilliant and prismatic :
margins rounded at each end, much broader at the side
furthest from the beak, very slightly curved in front, and
somewhat angular at the back : beaks prominent and projecting
beyond the dorsal margin, placed nearly in the middle, but a
little towards the narrower end of the shell : hinge-line curved,
occupying about one-fourth of the circumference : cartilage
small and slight, light horncolour, placed close to the beaks on
the narrower or posterior side : hinge-plate narrow, incurved
or excavated in the middle : teeth as in L. squamosum, but they
are more developed and lie more compactly, the cardinals are
more oblique, and the laterals are smaller, and placed nearer
the hinge-line in consequence of the groove which contains
these teeth being narrower and deeper in proportion to the
size of the shell : inside highly iridescent, and microscopically
striated lengthwise; margin plain: scars distinct. L. 0*1.
B. 0-125.
Var. 1. convexa. Shell rather more convex, and coarsely
Cat. Moll. ISorth.
pit-marked throughout. L. convexum, Alder,
k Durh. p. 93 ; F. & H. ii. p. 102, pi.
xxxvi. f. 10.
Var. 2. lineolata. Shell rather natter than usual, and marked
with minute longitudinal lines.
Yar. 3. ^>?s*Y?z'«7?s.
Shell triangular and convex, resembling
in shape Pisidium pusillum (var. obtusalis), marked with exceedingly
minute wavy ribs, which are formed by the confluence
of the pit-marks.
Habitat :
Gravelly sand on most parts of our coast
from the Shetland to the Channel Isles, in from 10 to
90 fathoms : although local,
it is not uncommon. It is
a Coralline Crag fossil. Var. 1. Equally diffused in a
recent state. Var. 2. Loch Fyne (M'Nab) ; Exmouth
(Clark) ; Guernsey (J. G. J.). Var. 3. Torbay (Web-
ster). The typical form has been found by Malm on the
Swedish coast in 20-50 fathoms, and by myself in the
Gulf of Spezzia in 18 fathoms. Sars has noticed its oc-
currence in postglacial beds in the Christiania district.
According to Mr. Clark the anterior part of the animal