ON GASTEROPODA. oo 
swim with peculiar elegance, by means of their fin and tail. 
It often happens that they are mutilated, a circumstance 
which has occasioned some confusion in the distinction of 
species. 
In the order PECTINIBRANCHIA, the animals of the first 
genus TURBO, are marine; they live on the sea-coasts, in the 
midst of rocks beaten by the waves, and consequently at no 
great depth of water. At low water, when the rocks are un- 
covered, these animals often remain fixed in the same place, 
but they are also sometimes seen to move, endeavouring with- 
out doubt to regain the sea. On the least touch they suffer 
themselves to fall, and thus easily escape from their enemies. 
Their locomotion is not rapid, which is certainly owing to the 
shortness of their disk. ‘Their nutriment should be vegetable, 
if we may judge by the apparatus of their mouth; but of this 
we are not perfectly assured. 
Weare ignorant of all the particulars of their reproduction ; 
we merely know that the sexes are distinct, and not combined 
in the same individual. The small species with corneous 
operculum are ovo-viviparous. ‘Thus these animals do not 
deposit corneous eggs like the siphonobranchia. It yet re- 
mains a question whether there are any true turbines with 
calcareous operculum. 
The animals of this genus are of some utility to the human 
species. In fact the inhabitants of the sea-coasts feed upon 
the smaller species, and from the larger a very fine nacre, or 
mother-of-pearl, is derived. Formerly, ornaments were made 
for cupboards of the shell of the ZT. marmoratus, completely 
stripped of its non-nacreous stratum. 
The animal of the SCALARIA is but very incompletely 
known. From the figures given by some authors, we conclude 
that it does not differ much from the animals which inhabit 
other operculated shells of the same order. From a figure 
communicated by Dr. Leach to M. de Blainville, it would 
VOL, XII. Aa 
