70 MOLLUSCA. 
at both ends, with a foot greatly elongated and adapted 
for boring in the sand, in which they live in from 60 to 
600 feet of water on the sea-coast. The sexes are dis- 
tinct. The young pass through several changes before 
assuming the adult form. The shells form the wampum 
of the Indians. 
Class IV.—Squins, etc. (Cephalopoda, head-footed). 
General Characteristics. — The Cephalopods are the 
highest forms of mollusks. They are marine, and either 
swim or crawl; have long arms or tentacles arranged 
about the mouth, armed with suckers or hooks, two par- 
rot-like beaks, and a toothed tongue. They generally 
possess ink-bags; have highly developed eyes, and a large 
brain protected by a cartilaginous covering, calling to 
mind the cranium of vertebrates. 
Wing - footed Cephalopods (/¢eropoda). — These, 
the lowest and perhaps degenerate Cephalopods, are free- 
swimmers, moving by two broad fins or wings upon each 
side of the neck (Fig. 65, P). In Northern waters they are 
found in vast swarms. The Cleodora emits a soft, clear, 
phosphorescent light that gleams through the delicate shell. 
The Cio, in swimming, almost touches its fins above and 
below. It has a wonderful arrangement for seizing prey. 
Each tentacle bears about 3,o00 transparent cylinders, 
each containing twenty stalked suckers ; and, as there are 
six tentacles, the C/o can grasp its prey with 360,000 hands. 
They have also a pair of many-toothed jaws, and a tongue 
armed with recurved teeth—a terrible array for so small a 
creature. They are eaten by whales. The young pass 
through several changes. 
Order I. Four-gilled Cephalopods (7Z¢trabranchi- 
ata); Nautilus (Vautilide)—Of 1,500 species that have 
lived in past ages, only two are extant. The shell (Fig. 75) 
is pearly, and divided into cells or rooms that are formed 
