266 COMPARATIVE ZOOLOGY. 
beautiful Ear-shell (4Zalzotis), frequently used for orna- 
ments and inlaid-work. 
In the higher Prosobranchs, the gills are comb-shaped 
and the sexes are distinct. The group includes all the 
spiral univalve sea-shells, and a few fresh-water shells. 
Many have the aperture entire, which is closed with an 
operculum: as the dull-colored Paludina and Melania 
from fresh water, and the pyramidal Zvochus, pearly 
Turbo, screw-like Turritella, common Periwinkle (Lz¢- 
torina), and globular Vatica from the sea. Others, the 
highest of the race, have the margin of the aperture notch- 
ed or produced into a canal, and are carnivorous and ma- 
rine: such are nearly all the sea-shells, remarkable for 
their beautiful forms, enameled surfaces, and brilliant 
tints, as the Cowry (Cyprea), Volute, Olive, Cone, Harp, 
Whelk (Buccinum), Cameo -shell (Cassis), Rock - shell 
(Murex), Trumpet-shell (Z’riton), Spindle-shell (/’usws), 
and Wing-shell (Strombus). 
Crass VI1.—Cephalopoda. 
The Cephalopods stand at the head of the subkingdom, 
some of them outranking the highest Articulates; but they 
are not so typical as the Gasteropods. The head is set off 
from the body by a slight constriction, and furnished with 
a pair of large, staring eyes, a mouth armed with a rasp- 
ing tongue and a parrot-like beak, and eight or more ten- 
tacles or arms. The body is symmetrical, and wrapped in 
a muscular mantle. 
The nervous system is more concentrated than in other 
Invertebrates; the cerebral ganglia are even inclosed in 
a cartilaginous cranium. All the five senses are present. 
The class is entirely marine (breathing by plume-like gills 
on the sides of the body), and carnivorous. The naked 
species are found in every sea. Those with chambered 
shells (as Vautilus, Ammonite, and Orthoceras) were once 
