Gasteropoda. - 



-5I0LLUSCA.- 



-TUITOSID^. 



331 



oblong, and has its nucleus in the middle of the inner 

 edge. The shell is ventricose, somewhat globular, and 

 the wliiils 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 very large, 

 and, indeed, comptise amongst them some of the 

 largest known Gasteropoda. Thej' form a very natural 

 group, and princi[)ally inhabit the warmer regions of 

 the globe. The species are rather numerous, thirty- 

 four having been described, and the}' are distributed 

 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 bod}' 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 cameo 

 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., figures on a dark gi'ound. In the 

 economic collection of shells in the British Museum, 

 for instance, we may see cameos carved on the shell of 

 the Horned Helmet from Madagascar, Cassis cornuta, 

 showing wliite figures on an orange ground ; on the 

 Black Helmet Shell, as it is called. Cassis Madarjas- 

 cariensis, from the West Indies, and on C. tuherosa, 

 eliowing white on dark claret colour ; and on the Red 



Fig. 217. 



Red Helmet Shell or Bull's Moutli (Cassis rufa). 



Helmet Shell or Bull's Mouth, C. rii/a, from tlie 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 jier- 

 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 tlie 

 period mentioned above there were used in France 

 nearly one hundred thousand Helmet Shells alone, of the 

 value of upwards of £8000. Of the different kinds, the 

 greatest number were the Bull's Mouth (^Cassis nifa), 

 which amounted to eighty thousand, the avemge price 

 being Is. 8d each, equal to £6400. Next to these 

 were the Black Helmet (C Madagascariensis), 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 canieus 

 is about £8000, giving a total value of the cameos 

 produced in Paris for 1846 of £40,000 1 



Family— DOLIIDiE. 



Tlie family of the TUN SHELLS [DuUida) 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 Dolium. — The genus Dolium (from the 

 species of which the English name Tun 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 maikod 

 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 pillar lip ratlier 

 twisted, and the canal short and suddenly curved 

 backwards. One of the largest species, Dolium (jcdea, 

 inhabits the Mediterranean. Some of the species are 

 found on reefs. 



Family— TRITONID J];. 



The family of TRUMPET SHELLS [Tritomda:) con- 

 tains a large number of species, about one hundred 

 and fifty having been described as living at the present 

 day. Tliey range from low water to fen or thirty 

 fathoms, and are distributed through the McditeiTa- 

 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 cohimolla 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. 



