J. D. MACDONALD ON METAMORPHOSIS OF GASTEROPODA. 71 
Having thus fallen in with the genus which I believe to be the adult state t&Broicuia, 
I transcribe its characters from rough notes taken at the examination of the solitary 
example alluded to : 
" Shell thin, membranous, depressed, paucispiral, with an open columella, communi- 
cating with a shallow and expanded aperture ; completely inclosed in a thick outer mantle 
covering the back. This mantle may be described as a convex, mushroom-like shield 
investing the shell and viscera, and arching over the whole foot and head, with an emar- 
gination in front, admitting of the protrusion of the latter, and corresponding with the 
true mantle opening. 
" A combed gill is distinctly visible in the mantle cavity, and the genital and excre- 
tory orifices are also included, on the right side. The foot is elongate, truncated and 
dilaminated in front, but flat and pointed behind, lying altogether in a depression within 
the thick margin of the epipodial shield. Tentacula conical, flattened, arising from i lie 
angles of a thin frontal lobe overlapping the muzzle; the ocelli placed behind the tenta- 
cula and close to the outer side of their base. 
" The muzzle appears to be proboscidiform, and the mouth is armed with two strong 
lateral labial plates, jagged in front and united in a hinge-like manner in the middle lint'. 
" Lingual ribbon of moderate length, triserial, with arched rachidian plates, armed with 
small teeth recurved from the anterior convex border. The uncini are sickle- shaped, ser- 
rulated internally and externally, and interlock over the rachis as in Brownia. Spherical 
otoliths are contained in the acoustic sacs ; and the sexes appear to be distinct ; but of this 
I cannot be certain, having had but a single individual to examine, which had been for 
some time preserved in spirits." 
The animal is very different from Natlca and its allies, and I know of no family into 
which it may be with propriety received, except perhaps the Velutinidce*. Its true posi- 
tion appears to me to be between the Muricklce and Ranellidce, and side by side with 
Velutina. 
I have already figured and described a little larval Gasteropod, having a subglobular 
cartilaginous case including the true spiral shell of the animal ; and to this I have to add 
another and very beautiful species, of which we obtained several specimens off the Wreck 
Reef. In this instance the transparent outer case is subcylindrical and spirally fluted, 
one flute commencing at the apex, and then crossing the others obliquely, so as to form 
the principal part of the columellar lip, which is completed by a prominent and slightly 
involute process near the base of the slit-like aperture. The little contained animal, with 
its spiral shell and operculum, is distinctly visible within ; but, as in the other examples 
noticed, the shell is so thin as to require additional protection in the morning of life. It 
must be stated, as furnishing one link in the series of changes here supposed to take place, 
that considerable numbers of the empty cases, rejected by their former occupants, are 
occasionally to be met with— a fact which I particularly observed at the Conway Reef. 
As to the mode of development of these curious structures I have but little to say. From 
the comparison of numerous specimens, it appears to proceed pari passu with that of the 
(?), which latter I an 
remove. 
