668 ME. WALTER GAESTANG ON COLPODASPIS PtrSIlLA. [NoV. 20, 



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 Cypnea europcea — 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 Oepha- 

 laspidea in the pleuropodial expansions of its foot (cf. Haminea), 

 in the posterior appendage of the mantle {Haminea, Fhiline), 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 

 Colpodaspis and PUurohranchus. These various points of resem- 

 blance are all explicable if we regard Colpodaspis as a very primitive 

 type of Tectibranchiate mollusk, belonging indeed to the Cephal- 

 aspidea, but retaining in an unspecialized condition an unusual 

 number of those primitive characters which the common ancestors 

 of the Cephalaspidea and Notaspidea alike possessed. It supplies 

 an indubitable connecting-link between these two great subdivisions 

 of the Tectibranchia ; but it belongs to the group Cephalaspidea, 

 in spite of the inappropriateness of the name, owing to its acquisi- 

 tion 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 

 described by Sars and myself has assumed its adult features. 

 Fischer' has suggested that Colobocephalus costellatus and Colpo- 

 daspis pusilla are possibly only young stages of Philine or of 

 neighbouring genera of Tectibranchs, owing to the radula in these 

 two types resembling very closely the radula of certain species of 

 Philine {velutinoides, lima, angulata). This theory, however, is, in 

 my opinion, altogether untenable in the case of Colohocephalus, 

 which, beyond the radula, presents no particularly Cephalaspidean, 

 or even Opisthobranchiate, features. The probability, on the other 

 hand, that the Philinidae have been derived phylogenetically from 

 a Colpodaspis-\ik& ancestor is sufficiently great to render Fischer's 

 view in this case worthy of consideration. The white colour of 

 the body and the early enclosure of the shell by the mantle 

 support this view ; but the fact that all the specimens so far taken, 

 which have been captured at such different times of the year as 

 June, August, and February, have been practically identical in 

 structure, and have shown no special approach towards the adult 

 organization of Philine, seems to me to render the view improbable. 

 The possession of a similar radula by so different a creature as 



1 ' M&nuel de Conchyliologie,' 1887, p. 564, 



