_Parietes and basis not porose. Scutum and Tergum with very small
articular ridges. Tergum broad, almost equilateral._
_Hab._--Attached to a Gorgonia, Tubicoreen, near Madras, (Dr.
Johnston). Hab. unknown, Mus. Cuming.
_General Appearance._--I have seen only two specimens, kindly sent me
by Dr. Johnston, and a single specimen in Mr. Cuming's collection.
In most points this species agrees with the two last species. The
shell (excepting the rostrum), and even the opercular valves in Mr.
Cuming's specimen were of a very fine purplish-red; in the other
specimens they were feebly tinted purple. The parietes are strongly
ribbed internally, and are not permeated by pores. The basal cup is
not porose, but its inner surface is ribbed in lines radiating from
the centre, and in both these respects this species differs from the
two foregoing. The Radii are rather narrow; they are paler coloured
than the parietes; they have their sutural edges plainly crenated.
The alæ have extremely oblique summits; the narrow rim added during
the diametric growth of the shell is white, the rest of the sheath
being, in Mr. Cuming's specimen, finely coloured like the parietes.
Basal diameter of the longer axis of the largest specimen, .4 of an
inch.
_Scutum_, rather narrow, with the basi-tergal corner much rounded
off; externally the lines of growth are little prominent. Internally,
the articular ridge is extremely little developed, and not at all
reflexed; there is no adductor ridge; there is a minute pit for the
lateral depressor muscle, placed almost on the edge of the valve.
The _Tergum_ is broad, forming (the spur being excepted) an almost
equilateral triangle. The articular ridge is remarkably little
prominent, and placed close to the scutal margin. The spur is nearly
half as broad as the valve, with its extremity or basal margin in one
case obliquely truncated, and in another case nearly square.
_Animal's body_ unknown.