MOLLUSCA. 



CLASS II. PTEROPODA.* 



THIS Class contains a very few animals of small 

 size, that swim in the ocean, but, having no feet, 

 are unable to fix themselves to any object. Their 

 organs of motion consist of a large broad wing-like 

 expansion, placed on each side of the head. They 

 have no shell; but enliven the surface with their 

 appearance in fine weather, where in immense hosts 

 they float about, dancing merrily along and direct- 

 ing their course by means of their fleshy head-fins. 



CKo.j 



Minute as are the creatures now under our notice, 

 they perform no useless or inconsiderable part in 

 creation, for, from their vast numbers, they make 

 the surface of the dreary Arctic sea alive with their 

 gambolings, while they supply a large portion of the 

 subsistence of the great northern Whales, whose 

 mighty jaws engulph thousands at a time. The pre- 

 sent genus is the only one we can pause to describe in 

 this Class, and the species we select is the best 

 known, the Arctic Clio (C. Borealis). It is about 

 an inch in length, oblong, without shell or mantle ; 

 the two pretty wing-like fins by which it moves are, 

 it seems, but a single organ, being connected by 



* Urtgov, pteron, a wing, and <rov;, pons, a foot, 

 t The name of one of the Muses. 



