234 SUPPLEMENT 
ber, and their distribution into the different parts of the world. 
It may be said, in a general manner, that no part of the earth 
is without marine mollusca, terrestrial, lacustral, or fluviatile ; 
and that the proportion of the species of these divisions must 
be in relation with the extent of the seas, the continents, the 
lakes, and rivers. 
We may be also assured, that almost all the families exist 
in the different zones of the globe, but that the genera and 
species of some are much more numerous in one zone than in 
another. Thus it would appear that there exist every where 
octopi, sepie, and loligines. It is difficult to be so certain 
respecting the genera of polythalamous shells; and in fact the 
only two of which the animals are a little known, spirula and 
argonauta, belong to the torrid zone. ‘The genera of sipho- 
nobranchia are also found in all latitudes, but there are many 
of the subdivisions which have been established on the shells 
of this order, which only belong to the intertropical regions ; 
such are the pleurotoma, tonna, lyra, vis, mitra, strombus, 
cones, oliva, porcelaines, and ovula, genera of which scarcely 
a species is known in our northern seas, and two or three only 
in the ocean and the Mediterranean. The number of the 
generic subdivisions of shells, of which species are wanting in 
the order of the asiphonobranchia, is not very considerable, or 
they are represented one by the other, so little do they mutually 
differ. We also possess all the genera of the families which 
compose the order of pulmobranchia, and they are found spread 
over all the earth, only in proportions a little different. Thus 
the species of the family of auriculacea are much more rare, 
and smaller, in our climates, than in the torrid zone. It is 
the same with the agathine and bulimi, dismemberments from 
the genus helix. The limnez appear, on the contrary, more 
numerous, and even larger, in our climates, than in the warm 
countries, which is not the case with the genera planorbis and 
physis. We have no species of onchidia or veronicella which 
