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 raduia 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. Pl]. Pleuropodial expansion; T. Tentacles. 
Fig. 5, 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 ; pl. 9, fig. 8. 
Shell pellucid, colorless, somewhat rigid (when dried ashy-whit- 
ish, subpellucid, shining), subglobose, wider than high; whorls 3, 
the last large, ornamented 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 
