9 GENUS DOLIUM. 
operculum. ‘The generative organ of the male is very retrac- 
tile, as in the Buccinum. 
Almost all the species which form the genius Dot1um were 
considered by the old conchologists, and particularly by Lin- 
neus, as Buccina, on account of the general relations by which 
these shells are allied. This author brought together those 
which we are now describing, so as to form a small separate 
group, which he placed at the head of his great genus, Bucct1- 
Num, placing those of the genus Cassis immediately after them. 
Before him, however, d’Argenville, by observing the identical 
form of these shells and their marked distinction from those 
species with which they had been confounded, first thought of 
separating them, and distinguished them by the name of Doxium. 
But it was Lamarck who clearly settled the bounds of this sepa- 
ration, and presented to conchologists the precise formation of 
the genus, ever since established in science. Indeed, the shells 
which it contains have so peculiar a form, that it would be diffi- 
cult to mistake them..: 
The genus Do.tium comprehends a small number of species, 
some of which attain so remarkable a growth, that they are 
sometimes as large as a man’s head. In fact the general ap- 
pearance of the shell, of an inflated, thick-set form, calls up the 
image of a tun, whence is derived its generic name. ‘Thus, the 
characters which make up these species are a form more or less 
inflated, girdled, and very globular ; the spire being much shorter 
than the lower whirl, causes the size of the aperture, which 
almost always occupies two thirds of the length of the shell. 
Denys de Montfort, in his Conchyliologie Systematique, has 
divided the Tuns into two groups; he comprised in the first the 
umbilicated species, which he called Perprx; the second in- 
cluded the Doxrum, properly so called, that is to say, the non- 
umbilicated species. This distinction, which is merely appa- 
rent, is produced by the development of the left lip; for the um- 
bilicus always exists, although more or less distinct. Cuvier, 
in his Animal Kingdom, retained the two divisions of Montfort ; 
but, according to his system, he still makes the Dorium one of 
the numerous sub-genera of Buccinum, thus bringing them back 
