208 



POPULAR CONCHOLOGY. 



the Pneumodermon and Clione are the slowest. They 

 appear, not only in calm weather, on the surface of the 

 sea, but may be caught in myriads on a stormy night. 

 An idea may be formed of their number when it is recol- 

 lected that the Clione borealis forms the main aliment of 

 the Greenland whale. 



The food of the Pteropoda consists of other oceanic 

 Molluscs which they can overpower, and small crusta- 

 ceans; the larger species of Clio eat, for example, the 

 young of Atlanta; Clione borealis devours the Limacina 

 arctica, &c. The Pneumodermon seize their prey with 

 their tentacula, armed with suckers. It is singular that 

 no observer has yet found any individuals with eggs, nor 

 any young among them. 



Mr. Forbes thus opens his article on Pteropoda: — " In 

 warmer seas than those which encircle our islands, the 

 surface of the water, when the weather is calm, and the 

 sun is shining, glistens with glassy needles, or shelly 

 bubbles. These upon closer examination prove to belong- 

 to curious Molluscs, which, instead of creeping over sub- 

 marine rocks and weeds, or burying themselves in the 

 soft mud and sand of the sea-bed, aspire to a gayer and 

 more sportive life, and play the part of Neptune's bees 

 and butterflies. From our less congenial waves they are 

 almost altogether absent, only a few stragglers, and those 

 with one exception of microscopic dimensions, have met 

 even the scrutinising eyes of practised naturalists." 



As the shell is sometimes present, sometimes absent, 

 the Pteropoda may be divided into two orders: Theco- 

 somata, with a shell, and Gymnosomata, without one. 



