PLIiUROBUANClIIATA. JIOLLUSCA. ApLl'SIADAi. 349 
Order L— PLEUEOBRANCHIATA. 
This order contains eleven families, but, with the 
exception of the Bubble-shells, none very numerous 
in species. The shell is spiral ; and both larvae and 
adult are shell-bearing. The larvae are furnished with 
deciduous cephalic fins. The animals have the foot 
elongate, adapted for walking. 
The old genus Bulla of Lamarck is now split into 
many, and even forms several families. The animals 
are all characterized, however, by having the tentacles 
broad, forming a more or less expanded frontal disk. 
As Mr. Hancock observes, this frontal disk is in fact 
nothing else than the dorsal and labial tentacles fused 
into one continuous mass. They are all carnivorous 
in their habits, swallowing their prey entire ; and their 
stomach is furnished with a muscular gizzard armed 
with calcareous plates. A fuller description of this 
organ will be found under the genus Scaxihander. They 
have no operculum. 
Family— PHILINIDHi:, 
Some of the species of this family have no shells ; 
others have a thin, fragile, ovate shell, which is con- 
volute and covered by the mantle. 
Genus Scaphandek. — See Plate 4, fig. 1 {Sca- 
phander Ugnarius, shell and animal). This genus has a 
distinct shell, not covered by the mantle. It is ovate, 
convolute, and spirally striated ; the spire is concealed, 
and the aperture is large, much expanded in front, and 
narrow behind. The animals are blind, and the giz- 
zard is formed of two large trigonal calcareous plates, 
and a small, narrow, transverse plate. This gizzard 
was described by Gioeni as a genus of shells ! The 
Rev. Mr. Landsborough has described it very well in 
the Scaphander Ugnarius, at the same time giving an 
account of the habits of this species, which is found on 
many parts of our sea-coasts. “ This gizzard,” he 
says, “ is a wonderful piece of mechanism, which one 
would not expect to find in the interior of a very soft 
mollusc. I thought it was composed of two plates, 
but I found there were three. Two of the plates are 
triangular, and placed one above the other, like the 
upper and nether millstones. They are quite flat, 
but a little concave externally, and rather convex 
internally ; they are bound together by strong carti- 
lage, and on one of the sides of the triangle there is a 
third valve or plate, giving strength to the cartilage, 
and keeping the two grinders at some distance, except 
at the centre, where the convex points meet, and thus 
leaving, except at these points, room for the reception 
of food in the triangular space between the two mill- 
stones. The food of the Bulla (Scaphander) seems to 
be the fry of other shell-flsh. Though they seem to 
indulge very freely as to quantity, they appear to be 
wiser than our biped gourmands, for they keep to one 
dish. In every one of the specimens I procured, the 
capacious gullet was filled with the fry of Mactra 
subtruncata. The gullet was in the form of a corn- 
sack, quite distended ; for each contained some scores 
of these little bivalves in an unbroken state. The 
sack, however, gradually emptied itself into the giz- 
zard ; and in this shelly mill the shells and their con- 
tents were reduced to powder, or rather fine paste, 
well fitted, we doubt not, to be wholesome nutriment 
for the industrious little marine miller.” 
Family — BULLIDAl (True Bubble-shells.) 
This family as now restricted consists of shells which 
are involute, exposed or external, or only partially 
covered by the reflexed lateral lobes of the foot. 
Genus Bulla. — In this genus the shell is ovate or 
subglobose, convoluted, solid, smooth, and variously 
coloured or mottled ; the spire is small, sunk, or hid- 
den, causing the apex to be perforated, and the aper- 
ture is longer than the shell, and rounded at each end. 
The animal has a large lobe or disk, truncated in front, 
bilobed behind, the eye immersed, subcentral, and the 
foot short and subquadrate. — See Plate 4, fig. 1 
(Alcera carnosa). The gizzard is furnished with three 
plates. The species are rather numerous, about fifty 
having been described. In their habits they are 
recorded as being found on sandy mud flats, slimy 
banks in estuaries, and in brackish water near the 
sea. At low water they may occasionally be seen 
concealing themselves in the mud or under sea-weed, 
where they have been observed exuding large quanti- 
ties of mucus to maintain the moisture of their skin. — 
(Adams.) Their food consists of small bivalve shells, 
which they are able to crush and triturate by means of 
their powerful gizzards. 
Family— AMPLUSTRIDH5. 
The species of this family have an oval, ventricose 
shell, ornamented with highly-coloured bands or mark- 
ings. The spire is generally conical and blunt, the 
aperture oblong or ovate, and more or less channeled 
in front. 
Family — APLYSIIDHH (Sea-hares), 
The Sea-hares have the shell internal, covered by 
the mantle, or it is wanting altogether. The animals 
are slug- like in form; have the head produced, and 
their ear-like tentacles separate, and slit externally. 
The foot is long, drawn out into a tail behind, and has 
large side lobes reflected over the back. The' gizzard 
is armed with horny spines. 
Genus Dolabella. — In the animals of this genus 
the side lobes of the foot are not expanded so as to 
enable the creature to swim, and the shell is hard, cal- 
careous, of a triangular shape, and with a curved and 
callous apex. See Plate 4, figs. 3, 4 (Dolabella Rum- 
phii). 
Genus Aplysia. — In the animais of this genus the 
