Pvn H,i I'UitlS

14 TEREBRATULID.E.
slight ears, or triangular expansions, at the upper angles
of the lower valve, as in T. caput -serpentis ; and they
are furnished with a very distinct and prominent crest
or ridge, placed inside and nearly in the middle of this
valve, resembling, except in position, the marginal plate
of Argiope cistellula. This last-mentioned character
likewise occurs in T. septata, Philippi, a Sicilian fossil
(T. septigera, Loven) , and is remarkably developed in that
species ; but the foramen is incomplete in T. cranium,
and entire in T. septata. Some specimens of T. cranium
have the front margin more or less truncate, and others
have slight and blunt ridges or angularities extending
lengthwise to the front margin.
B. Shell longitudinally striate : skeleton composed of two short
ribs, which are looped and form a kind of ring. (Terebratidina,
D'Orbigny.)
2. T. caput-serpen'tis *, Linne.
Anomia caput-serpentis, Linn. Syst. Nat. ed. 12, p. 1153. T. caput-ser-
pentis, F. & H. ii. p. 353, pi.
lvi. f. 1-4.
Body light orange-yellow : mantle thickened by calcareous
spicula ; tentacles extensile and pencilled, with a crimson
tubercle at the base of each : arms bright orange, inclining to
a crimson hue ; muscular stem thick ; cirri long, ciliated all
over, and arranged in a single row : peduncle rather short,
of numerous loose tubular fibres.
composed
Shell lyre-shaped, very variable in respect of length and
breadth, sometimes nearly round and at other times oblong,
convex in the middle but compressed towards the front and
sides, rather solid, of a dull aspect : sculpture, scored by numerous
longitudinal striae or fine ribs, which radiate from the
beak to the outer margins, becoming occasionally tuberculate
where they are crossed by the hues of growth ;
some of these
striae are forked, or divaricate, being simple and stronger near
the beak ; the surface is closely studded with microscopical
points, each resembling the bottom of a homoeopathic bottle,
* From its resemblance to a snake's head.