40 
THE LIVING WORLD. 
The Swimming Snail (. Pterotrachea ) is a wing-footed mollusk allied to the 
Cephalopods. The name is derived from portions of the feet being expanded 
and fitted for swimming. The two arms, corresponding to the head and tail, are 
The swimming snail ( Pterotrachea coronata). 
CLUB BEARING URCHIN. 
(Cidaris clavigera.) 
supplied with suckers like those of the cuttle-fish, while the body appears dotted, 
each dot, however, being a protrusible arm in which is a suction disc. Its 
length rarely exceeds one inch. 
Mouth-Closing Snail (Clausilia bi- 
plicita ). These are found about the margins 
of streams, but 
rarely enter 
the water, their 
principal hab¬ 
itat being in 
the neighbor¬ 
hood of the 
Mediterranean. 
They are wide¬ 
ly distributed 
over Europe, 
Asia and Africa 
and number 
seven hundred 
species. The 
shape is cylindrical fusiform, and the mouth appears 
sealed during dry seasons. 
Mussel Shell (Spondylus spinosus ). A very large 
variety is included under this head, the name being 
given to designate the thorny appearance of the shells. 
Among these is a very rare shell found in the East 
Indies under the specific name of the king mussel (N. 
reg ius ). 
The Rooted Hair Star-fish belongs to the order 
of Rhizo crinadce , which takes a place midway between 
the sea-urchins and snails. It is a deep-water dwel¬ 
ler, taken by dredge, at a thousand fathoms, in the 
A , 1 , • T y • & i L 1 . ’ ANTEDON CRINOID. 
Atlantic, it is somewhat rare now, but was very 
abundant in past geological ages. 
The Antedons, or Climbing Sea-Urchins, belong to the same species as 
MUSSEL SHELL. 
