UASTiiUoroDA. MOLLlJtjCA. Tuitonida,. 331 
oblong, and has its nucleus in the middle of the inner 
edge. The shell is ventricose, somewhat globular, and 
the w’hirls often marked with varices. The aperture 
is either elongate and narrow, or ovate, and the canal, 
in which is lodged the siphon of the mantle, is, like it, 
recurved. *The Helmet Shells are often veiy large, 
and, indeed, comprise amongst them some of the 
largest known Gasteropods. They form a very natural 
group, and principally inhabit the warmer regions of 
the globe. The species are rather numerous, thirty- 
four having been described, and they are distj'ibuted 
through several genera. 
Genus Cassis. — The genus Cassis (which gives the 
name to the family) has an oblong or subtrigonal shell, 
with a short, nearly flat spire, a long aperture or mouth, 
the outer lip of which is thick, reflected, and toothed 
within, the inner spread over the body whirl, callous and 
plaited ; the canal sharply recurved ; the operculum is 
oblong, narrow, and small. The animals are active 
and voracious. They live in shallow water, in sandy 
localities, often concealing themselves in the sand, and 
attacking the bivalve shells that abound in such places. 
The shells of some of the larger species are extensively 
used in the manufacture of cameos. Like most other 
shells, they are composed of three layers or plates, and 
these differ from each other in relative thickness as well 
as in colour. The central plate is generally the thickest, 
and is differently coloured from the outer. The canieo 
cutters appear to be well aware of this structure in the 
Helmet Shells and some others, and avail themselves of 
it in cutting their cameos, so as to produce white or 
rose-coloured, &c., flgures on a dark ground. In the 
economic collection of shells in the British Museum, 
for instance, we may see cameos carved ou the shell of 
the Horned Helmet from Madagascar, Cassis cornuta, 
showing white flgures on an orange ground ; on the 
Black Helmet Shell, as it is called. Cassis Madagas- 
cariensis, from the West Indies, and ou C. tuberosa, 
showing white on dark claret colour ; and on the Bed 
Fig. 217. 
Red Helmet Shell or Bull’s Mouth (Cassis rufa). 
Helmet Shell or Bull’s Mouth, C. rvfa, from the Indian 
seas- fig. 217 (which is the one most extensively used), 
showing pale salmon colour on orange ground. In 
1847 Dr. Gray, at a meeting of the Society of Arts, 
gave some very interesting details upon the subject of 
cameos. For many years the art of cutting cameos 
from shells was confined to Italy, but a little more 
than twenty years ago an Italian commenced making 
them in Paris, and in 1847 about three hundred per- 
sons were employed in that branch of trade in that 
city alone. The number of shells used in this manu- 
facture is immense ; and Dr. Gray stated that at the 
period mentioned above there were used in France 
nearly one hundred thousand Helmet Shells alone, of the 
value of upwards of £8000. Of the diiferent kinds, the 
greatest number were the Bull’s Mouth {Cassis rufa), 
which amounted to eighty thousand, the average price 
being Is. 8d each, equal to £6400. Next to these 
were the Black Helmet {C. Madaguscariensis), which 
amounted to eight thousand, averaging 5s. each, equal 
to £1800. The average value of the large cameos 
made in Paris is about six francs each, giving a sterling 
value of £32,000; and the value of the small cameos 
is about £8000, giving a total value of the cameos 
produced in Paris for 1846 of £40,000 ! 
Family — DOLIID..T]. 
The family of the TUN SHELLS {Doliidai) are known 
by their large, light, ventricose shells, marked with 
transverse ribs or furrows. The animal has the 
mantle inclosed, a very large foot, truncated in front, 
without an operculum. The species are not numerous, 
only fourteen or fifteen having been described, but 
many of them attain a large size. They are found in 
the Mediterranean, in Ceylon, China, Australia, and 
the Pacific. 
Genus Doliuji. — The genus Dolium (from the 
species of which the English name Tuii given to the 
family has been derived) has a rather delicate, light, 
nearly globular, and ventricose shell, with a short spire 
and a large ovate mouth. The surface is marked 
with spiral grooves or ribs, and the last whirl forms 
nearly the whole of the shell. The outer lip is more 
or less thickened, waved internally, the [tillar lip rather 
twisted, and the canal short and suddenly curved 
backwards. One of the largest species, Dolium galea, 
inhabits the Mediterranean. Some of the species are 
found on reel's. 
Family— TRITON IDHU. 
The family of TRUMPET SHELLS {Tritonidee) con- 
tains a large number of species, about one hundred 
and fifty having been described as living at the present 
day. They range from low water to ten or thirty 
fathoms, and are distributed through the Mediterra- 
nean, the West Indies, Africa, India, China, the 
Pacific, and Western America. The animals have a 
small foot, and an annular, ovate, or triangular oper- 
culum, with the nucleus subapical. The shells are 
ovate, with a conical spire, and are generally strongly 
marked with varices on their whirls. The aperture 
is ovate, the columella veined or grooved, and the 
canal in front is straight. This family contains two 
large genera, the shells of which differ from each 
other in the disposition of their varices. 
