LEPAS PATELLARIS, (_Gmelin_). _Spengler._ Schriften der Berlin.
Gesellschaft, &c. b. i (1780), Tab. 5; Chemnitz, Neues Syst.
Couch., Tab. 98, fig. 839.
_Shell depressed; brown, generally with obscure longitudinal violet
stripes: radii (in full-grown specimens) with their summits rounded and
surfaces finely ribbed parallel to the basis: basis sometimes permeated
by imperfect pores. Scutum internally with an adductor ridge._
_Hab._--Bengal, on wood, Mus. Brit.; on a shell, Mus. Stutchbury;
Philippine Archipelago (young specimen), Mus. Cuming. According to
Spengler, on the Coromandel and Malabar coasts.
_General Appearance._--Shell depressed, sometimes much depressed:
orifice elongated, rhomboidal, but little toothed; surface smooth,
but in old specimens sometimes with the walls slightly folded
longitudinally. The radii are rather narrow, with their summits
oblique; in old specimens their summits are rounded, and their
whole surface finely ribbed parallel to the basis. Colour, in old
specimens dirty brown, tinged with violet, sometimes in longitudinal
bands, and with whiter irregular marks in the upper parts owing to
disintegration: in young specimens the walls are regularly banded
longitudinally, with violet-brown and dirty white; the radii being
generally of a paler dirty red or violet. Basal diameter of largest
specimen .9 of an inch.
_Scuta_, externally rather smooth; internally, articular ridge
prominent, reflexed, with the lower edge hollowed out so as to be
slightly hook-formed: adductor ridge small; there is a slight pit
for the lateral depressor. _Tergum_, with the spur bluntly pointed,
placed at about its own width from the basi-scutal angle; there is no
longitudinal furrow, only a slight depression; carinal margin arched
and protuberant: internally, articular ridge extremely prominent,
running down in the direction of the middle of the spur: crests for
the tergal depressores well developed.
_Parietes_, with the pores rather large; the internal lamina is very
strongly ribbed, the ribs being but slightly denticulated at their
bases: the parietal pores do not appear to be crossed by transverse
septa: sheath closely attached to the walls. The radii have jagged
oblique summits forming an angle of about 45° with the horizon; in
old specimens they become more oblique and narrow: and are then
very remarkable from their summits being arched and rounded, with
a crenated edge, and with their whole surface transversely ribbed
in horizontal lines; this is likewise the case with the recipient
furrow in the opposed compartments: in young specimens the radii are
externally quite smooth: the septa on the sutural edges are bluntly
denticulated; the interspaces being filled up solidly. The alæ have
their summits oblique, but much less oblique than the summits of the
radii; their sutural edges are very finely crenated.
_Basis_ thin, either quite solid, that is, not permeated by pores,
but only furrowed in lines radiating from the centre, or permeated
by pores towards the circumference, the pores being of very small
diameter;--so that we here have an important character variable
within the limits of the same species. Base flat, and this holds
good, as remarked by Spengler, even when the specimens are attached
to cylindrical pieces of wood.
_Animal's body_ unknown.
_Affinities._--In the basis being sometimes permeated towards the
circumference by pores, and by the colouring (the other species in
this and the next section being dirty white), _B. patellaris_ has
almost as strong a claim to be ranked in the last as in the present
section: in the rounded summits of the radii, and in the state of
the basis, it, perhaps, shows more affinity to _B. improvisus_ than
to any other species; it is, however, almost equally allied to _B.
glandula_.