2 GENUSDOLIUM. 



operculum. The generative organ of the male is very retrac- 

 tile, as in the BUCCINUM. 



Almost all the species which form the genius DOLIUM were 

 considered by the old conchologists, and particularly by Lin- 

 naeus, 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, BUCCI- 

 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 DOLIUM. 

 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 DOLIUM 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 PERDIX ; the second in- 

 cluded the DOLIUM, 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 DOLIUM one of 

 the numerous sub-genera of BUCCINUM, thus bringing them back 



