MOLLUSCS. 



351 



tains but four living species, one of which, A. occidentalis, is occasionally found off 

 our northern coasts. Of its habits almost nothing is known. In the pelican's-1'oot 

 shell {A. pes-2)elecani) of Europe the outer lip is produced 

 into two or three long horns, like those of Pterocvra. 



The helmet shells, Cassid^e, are thick and heavy, the 

 spire is short, and the aperture terminates in front in a 

 short recurved canal, the columellar lip is covered with a 

 thick deposit of callus, and, like the other, is toothed or 

 ribbed. The animal has a large head, a long extensible 

 proboscis, and a large foot. These species are mostly 

 large and active carnivorous animals, feeding chiefly on 

 bivalve molluscs. Owing to the fact that the shell is 

 made up of differently colored layers, the helmet shell- 

 are extensively used in the manufacture of shell cameos. 

 "Genoa and Rome. are the seats of the Ijest work, al- 

 though many common ones are cut in France. In Rome 

 tliere are about eighty shell-cameo cutters, and in Genoa 

 thirty, some of whom also carve in coral. The art of 

 cameo cutting was confined to Rome for upwards of forty 

 years, and to Italy until the last twenty-six years, at which time an Italian began cutting 

 cameos in Paris, and now over three hundred persons are emi^loyed in that city. . . . 

 The shell is first cut into pieces the size of the required cameos, by means of diamond 

 dust and the slitting mill, or by a blade of steel [soft iron ?] fed with emery and water. 

 It is then carefully shaped into a square, oval, or other form on the grindstone, and 

 the edge finished with the oilstone. It is next cemented to a block of wood, which 



Fig. 459. — Aporrhais occidentalis. 



in, 41)1 — ( I Hi jjl i( I, liuliiK-t sliL-n. 



serves as a handle to be gras])ed by the artist while tracing out with a pencil the 

 figure to be cut on the shell. The pencil mark is followed by a sharp ))oint, which 

 scratches the desired outline, and this again by delicate tools of steel wire, flattened at 

 the end and hardened, and by files and gravers, for the removal of the superfluous 

 portions of the white enamel. A common darning-needle, fixed in a wooden handle, 

 forms a useful tool in this very minute and delicate species of carving. The careful 



