76 Mr. Montagu's Description of Marine Animals 
we ever remember to have seen it elsewhere, occupying every 
other deserted turbinated or spiral shell, from the smaMTurbo pidlus 
to the Buccinnm nndatum, it must be concluded that the adopted 
habitation of this Sipunculus is not suited to the form of that 
crab ; a matter of no small proof of the wise dispensations of an 
omnipotent power, the source of original instinct, with which ani- 
mals, even the most contemptible in appearance, are endowed for 
the preservation of their species. 
This animal further secures itself from the attack of other ene- 
mies by closing up the aperture of the shell (except a round hole 
sufficient for its body) with sand strongly agglutinated together; 
and this as far in the shell as is necessary for contracting it to the 
size required. Within this the larger or posterior part of the ani- 
mal, as far as the vent, is concealed in the spiral volution, pro- 
truding occasionally that part only which is capable of internal 
retraction. 
It differs from S. nudus in being much shorter and verrucose for 
a considerable space behind the vent, in not having so sudden a 
decrease in size before the vent, and in the fringe or feelers round 
the mouth being longer; it has also much greater retractile powers 
in proportion to its length, and when wholly receded within the 
shell is seldom above an inch and a half long. 
Laplysia viridis. 
Tab. VII. Fig. 1. 
With the fore part of the body like a commmon Limax ; tenta- 
cula or feelers two, flat, but usually rolled up, and appear like 
cylindric tubes ; at a little distance behind the tentacula, on each 
side, is a whitish mark, in which is placed a small black eye : 
the body is depressed, and spreads on each side into a membra- 
naceous fin, but which gradually decreases from thence to the tail, 
or 
