32 COLPODASPIS. 
the fact that the foot is attached to the body by a somewhat narrow 
stalk—a feature which it shares with most Prosobranchs. Gwyn 
Jeffreys even informed him that he was inclined to consider 
Colpodaspis as the young of Cypraa europea—a view which now, 
at any rate, can no longer be entertained. 
In spite of our ignorance of the anatomy of Colpodaspis we may, 
however, as a result of the above observations, be certain that 
Colpodaspis is a true Opisthobranch. It resembles various Cephal- 
aspidea in the pleuropodial expansions of its foot (cf. Haminea), in 
the posterior appendage of the mantle (Haminea, Philine), in its 
inflated shell (Haminea, Utriculus), and in its radula (Philine). On 
the other hand it resembles the Notaspidea, and differs from the 
above types of Cephalaspidea, in the great extent of the mantle and 
in the form of the head and tentacles. In the latter point it again 
resembles the Anaspidea, for in the young Aplysia, as I have often 
observed, there is only one pair of tentacles (the anterior one) for a 
considerable period, and these are grooved just as in Celpodaspis 
and Pleurobranchus. These various points of resemblance are all 
explicable if we regard Colpodaspis as a very primitive type of 
Tectibranchiate mollusk, belonging indeed to the Cephalaspidea, but 
retaining in an unspecialized condition an unusual number of those 
primitive characters which the common ancestors of the Cephalas- 
pidea and Notaspidea alike possessed. It supplies an indubitable con- 
necting-link between these two great subdivisions of the ‘Tecti- 
branchia; but it belongs to the group Cephalaspidea, in spite of the 
inappropriateness of the name, owing to its acquisition of pleuropodial 
expansions and a_ posterior pallial appendage—two associated 
features which are especially characteristic of this group. 
The question still remains open whether or not the creature de- 
scribed by Sars and myself has assumed its adult features. Fischer 
has suggested that Colobocephalus costellatus and Colpodaspis pusilla 
are possibly only young stages of Philine or of neighboring genera 
of Tectibranchs, owing to the radula in these two types resembling 
very closely the radula of certain species of Philina (velutinoides, 
lima, angulata). This theory, however, is in my opinion, altogether 
untenable in the case of Colobocephalus, which, beyond the radula, 
presents no particularly cephalaspidean, or even Opisthobranchiate, 
features. The probability, on the other hand, that the Philinidze 
have been derived phylogenetically from a Colpodaspis-like ancestor 
is sufficiently great to render Fischer’s view in this case worthy of 
