ON MOLLUSCA. 935 
appear to represent in the hot climates the limaces of our 
zone, as our testacelle replace the parmacelle of the torrid 
zone. In all the other families, naked or conchyliferous, we 
may almost generalize the same observation, in adding that 
the species of the same genera are much more numerous, and 
especially much larger in the equatorial than in the polar 
regions, and more especially than in ours. 
In the class of the acephalophora, we shall equally arrive at 
the same result. In the order of the palliobranchia, the lin- 
gule are only to be met with in India. We find terebratule, 
orbicule, and crania, in all countries. This is still more evi- 
dent respecting oysters, which are every where abundantly 
distributed. It is not the same with the tridacne, which are 
as yet known only in the Indian Archipelago. The pectines 
and lime are found in all seas. The umbelle, the pinne, and 
crenatulz, appear to belong only to the seas of warm climates. 
The mussels, and even the irregular auricule, are of all seas. 
It is the same with all the generic subdivisions of the family 
of arcacea, and of that of submytilacea. ‘The trigoniz, of that 
of camacea, have not yet been found living, except in the 
austral zone. Species of all the genera of conchs have been 
observed in all seas, but sometimes one of these genera is 
represented by another closely approximating. Thus our 
cyclades appear to be the cyrene in India, &c. It would also 
appear that the venus saxicava are found every where ; and it 
is the same case with the mactre. The myz appear rather to 
belong to the northern seas, as well as the pandore and some 
solens. The oval solens belong rather to the southern cli- 
mates. We find pholades every where, and probably tere- 
dines, while the fistulane, clavagelle, &c. are almost con- 
stantly of the equatorial zones. 
The simple or aggregate ascidiz exist also in all zones, but 
nevertheless more numerous, and more developed in the equa- 
