PROSOBRANCH GENUS PONTIOTHAUMA. 457 
from its shell when I received it and was rather broken, and the 
tissues were so exceedingly hard as to render dissection difficult ; 
moreover, the body-cavity had been cut into and the organs 
somewhat displaced. 
The general appearance of the animal, as contracted in spirit, 
is shown by the figures (Pl. 42. figs. 1,2, &3). The body had 
evidently been entirely devoid of pigmentation. The surface of 
the foot is minutely granulated ; but this may possibly be merely 
a post-mortem appearance. 
The foot is ovate and much elevated; it is expanded and 
slightly bilobed in front and pointed posteriorly ; and its anterior 
margin is very conspicuously duplicated. No trace of an oper- 
culum or opercuiar pad could be detected, neither was any pedal 
pore evident. The most remarkable feature of the external 
characters of this form.is that to which allusion has already been 
made, namely, the enormous rostral development. The snout, 
even in the contracted state, constitutes a very considerable pro- 
portion of the whole body of the animal; and its finely wrmkled 
appearance suggests that it is capable of even much greater 
extension. It is a perfectly cylindrical structure terminating 
anteriorly in a large disk which bears the wide, circular rhyncho- 
stomial opening at its centre. This rostral disk appears capable 
of enormous expansion, its margin in the retracted condition 
being elaborately frilled and crenulated. The tentacles are short 
and apparently blunt: they are borne upon the sides of the 
rostrum just posterior to the origin of its terminal disk, and they 
are situated in a horizontal plane slightly below that of the axis 
of the rostrum (PI. 42. fig. 2). No trace of eye-spots could be 
distinguished ; it would not, however, be safe to assert that eyes 
are entirely absent in this form, for, not wishing to entirely 
destroy the unique specimen, the question of their non-existence 
has not been definitely decided by sectioning the head-region. 
Although the example dissected is a female, a rudimentary penis- 
(P.) is present, and is situated immediately behind and a little 
below the right tentacle*. The mantle-margin is somewhat 
thickened, and it completely encircles the body, passing round 
the siphon and over the foot. The siphon (S.) is solid and fleshy, 
it is conical in form and is devoid of appendages. 
The pallial cavity can be completely subdivided into infra- and 
* The presence of a vestigial penis in the female would seem to be a nut 
altegether uncommon occurrence among Toxoglossates. 
23* 
