MOLLUSCS. 109 



them as the work approaches completion. "Shell-cameos some years ago 

 were a good deal in fashion ; and even now a well-executed, artistic Roman 

 shell-cameo is an elegant piece of art. Genoa and Rome are the seats of 

 the best work, although many common ones are cut in France. In Rome 

 there 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 upward 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 

 thousand persons are employed in that city." 



HETEROPODS. 



The heteropodous molluscs are but little known except to naturalists. — 

 a fact due both to their structure and their habits. They are almost per- 

 fectly transparent, and usually occur on the surface of the sea far from 

 land. Some, like the form figured on the plate, have no shell, while in 

 others it is well developed ; but like the rest of the animal it is perfectly 

 transparent. They are all predaceous in their habits, and play havoc with 

 the other surface-swimming forms. They swaM at the surface at night, 

 and at such times the fortunate naturalist who is situated ,so as to use a 

 surface-net on the high seas receives his reward in individuals of this and 

 the following group. 



PTEROPODS. 



The Pteropods, or wing-footed molluscs, are also pelagic ; that is, they 

 occur on the surface of the sea far from land. 

 Only occasionally do they occur near the shore, 

 and then their presence is to be explained by 

 peculiarities of wind or current. This w T as the 

 case where, a few years ago, the harbor of Port- 

 land was filled with specimens of Clione, a small 

 form about an inch and a half in length. This 

 species properly belongs to the far north, and 

 in the Arctic seas it forms large schools which 

 sometimes discolor the sea for miles. To the 

 whalers this form is known as ' brit,' and 

 through these schools the huge right-whales 

 swim with open mouth, straining out these 

 seemingly inconsiderable forms, and yet so 

 abundant are they that the whales can live fig. 103.- a Pteropodmoiiusc( raom?). 



„ i £ . which forms a large part of the food, 



anQ grow iat Upon them. or • brit, - of the whalebone whales. 



