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MOLLUSCS. 
the tritons, but they are broader, more globose, and have shorter spires. The 
aperture is more or less dentate on each side, and the siphonal canal short, and 
sharply recurved. Upon the columellar side the animal deposits a strong shelly 
callosity, which in some species is enormous, and unites with the outer lip above. 
The animal closely resembles that of Triton ; its dentition is similar, but the 
opercula in this family are peculiar, having a lateral nucleus, and often being 
rayed like an expanded fan. The shells of some species consist of different- 
coloured layers, and are made use of for carving shell-cameos, in order that the 
subject may stand out in relief upon a differently-coloured ground. This family 
includes the genus Cassis and its subgenera, and the genera Morio and Lambidium. 
Nearly all the species are from hot regions, but a few occur in Japan and New 
tun-shell, Dolium perdix (l nat. size). 
Zealand; and the well-known Mediterranean Morio tyrrhenus has of late years 
been dredged living in deep water off the south-west of Ireland. 
The tun-shells ( Doliidce ) are mostly thinnish and of globose form, sometimes 
of very large size, and always spirally ribbed and grooved. They have no varices, 
and are without opercula. The foot of the animal is large, and the retractile 
proboscis long, and furnished with an expanded disc at the end, as in the figured 
Dolium perdix. The shells of the subgenus Malea, which have the outer and inner 
lips strongly dentate, form a connecting link with the Cassididce. Nearly all the 
species, about fifteen in number, are tropical. Two, however, occur in the 
Mediterranean, and several in Japan; Dolium galea, which occurs off the south 
of France and other parts of the Mediterranean, has a shell 8 to 10 inches in 
length, and is the laigest gastropod of that region. This mollusc, as well as 
various species of Cassididce and Tritonidce, are said to secrete sulphuric acid. 
