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almost circular opening. The siphon is cut oft’ anteriorly by a narrow, high, irregulär wall,
diftering somewhat on the right and the left valve; communication between the siphon and the
larger anterior cavity of the shell takes place principally through a rather narrow, irregulär
opening situated at about the centre of this separating wall (this opening marked by* in the
adjoining figure) and on the left valve by means of a smaller opening situated dorsally (shown
by** in the figure mentioned). For further details about the structure of this separating wall
it seems to me most convenient merely to refer to the accompanying fig. LII. Dorsally a short
distance in front of this wall, tliere is on both the right and on the left valve a rather long and
somewhat irregulär peg, directed downwards and somewhat backwards. On the right valve
the hinge is furnished with a long, wing-shaped and rather strongly projecting tooth; this tootli
I «■*
Fijf. LII. — C. (Siphonostra) spinifera n. sp. — The posterior part of the shell seen from inside. 1. Right valve.
2. Left valve, juv. q.
suddenly ceases anteriorly, a striking, almost rectangular, corner is formed, and decreases
gently and uniformly in height posteriori}7. On the left valve there is a cavity
corre-sponding to this tooth. (In the accompanying figure 5 this tooth is only indicated
schematically by a curved line.) 1 did not succeed in finding any hinge tooth posteriori}’
either on the right or the left valve. The selvage is verv wide along the anterior and
posterior margins of the rostrum and along the posterior margin of the rostral incisur
-the incisur is quite filled by it — and along the anterior part of the ventral margin of
the shell; it continues along the whole ventral margin of the shell, extending somewhat
outside the edge. It is uniformly and finely cross-striated and is extremelv finely, almost
invisibly, serrated at the edge or else smooth-edged. The shell is presumably rather
strongly calciferous — although the type specimen had a soft shell, not calci ferous; a larva,
preserved in the same liquid as the type specimen, had in its shell mimerons rounded
calcaret ms concrétions.
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