Pvn H,i I'UitlS

432 MACTMD.E.
they live together and under such circumstances retain
their respective peculiarities. M'Andrew obtained both
at Malaga — L. elliptica on the shore, and L. oblonga by
the dredge, from 4 fathoms. In my cabinet is a curious
malformation, the specimen having
an inner case or
double shell on the posterior side.
The present species is the Mactra Mans of Pulteney,
L. solenoides of Lamarck (but not of Capt. King), M,
of Turton's l
L. Sole-
hyans Conchological Dictionary/
noidea of Brown, and probably L. solida of Philippi.
Leach separated it from L. elliptica under the generic
title of Psammophila.
Genus IV. SCROBICULA'RIA *, Schumacher.
PL VIII. f. 4.
Body oval, compressed : mantle open throughout
the ventral
range, somewhat thickened at its edges : tubes very long, sepa-
rate, each covered with a membranous sheath or outer case ;
orifices :
usually plain gills of equal size : foot long and flexible.
Shell triangidarly oval or oblong, nearly equilateral, thin,
of a uniform white colour, gaping at the posterior end, slightly
and concentrically striated : epidermis slight and iridescent :
beetles turned towards the posterior side, almost contiguous :
cartilage placed obliquely: teeth, two small cardinals in the
right valve, and one in the left valve, which is clasped by the
laterals laminar, not always developed in both
opposite pair ;
valves, and sometimes altogether wanting.
It is much more difficult to define this genus by a
correct name than by comprehensive characters. Natu-
ralists are perhaps over-fastidious in the former respect.
I should have been glad to recognize the claim of prior-
ity put forward by Mr. Searles Wood for Trigonella
(1778) if Da Costa's description would have justified my
doing so; but it evidently applied to Mactra rather
* Having a little trench ; so called from the shape of the cartilage-pit.