COLOBOCEPHALUS. 33 



consideration. The white color 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 differ- 

 ent 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 Colobocephalus rather minimizes than supports the 

 view which Fischer has expressed. 



Fig. 1, Colpodaspis pusilla, from Plymouth. Dorsal view of the 

 animal creeping upon a flat surface; enlarged. F. Foot; M. 

 Mantle enclosing shell ; P. Pallial appendage ; S. Pallial siphon. 



Fig. 2, Ventral view of same, as creeping inverted on the surface- 

 film. PI. Pleuropodial expansion ; T. Tentacles. 



Fig. 3, Half row of radula-denticles. 



Figs. 4, 5, The shell, much enlarged. 



Genus? COLOBOCEPHALUS Sars, 1870. 



Colobocephalus M. SARS, Bidrag til Kundskab om Christiania- 

 fjordens Fauna, II, p. 56. 



Shell subauriform, very thin, submembranous, with inconspicuous 

 epidermis or none ; spire small, the suture deep ; aperture very 

 large ; ends of peristome disunited ; columella flexuous ; no oper- 

 culum. 



Animal not completely retractile into the shell; head with vertical 

 revolute tentacular processes ; no tentacles ; eyes sessile on neck ; 

 foot with anterior-lateral processes, the sole large and oblong, trun- 

 cated behind, having a median lengthwise furrow ; mantle not re- 

 flexed over the shell. Radula as in Philine. 



A form of problematic relationships, which Fischer surmises may 

 be the young of Philine. 



C. COSTELLATUS M. Sars. PI. 21, figs. 6-12 ; pi. 9, fig. 8. 



Shell pellucid, colorless, somewhat rigid (when dried ashy-whit- 

 ish, subpellucid, shining), subglobose, wider than high ; whorls 3, 

 the last large, ornanfented with low, narrow, longitudinal, somewhat 

 sigmoid riblets. Spire very short and obtuse. Aperture longitu- 

 dinal, ovate ; columellar lamina very thin, revolute over the wholly 

 covered umbilicus, then visibly narrowed, produced, and continued 

 3 



