298 THE INHABITANTS OF THE SEA. 
imported into France, and the value of cameos produced in Paris 
alone amounts to more than a hundred thousand pounds. A large 
number are also cut in the small town of Oberstein on the Nahe 
(a river flowing into the Rhine at Bingen), which has long been 
famous for the manufactory of agate ornaments and trinkets, 
and has now added this new branch of industry to the more 
ancient sources of its prosperity. 
The Pteropods, or Wing-footers, move about by means of 
two fin-like flaps, proceeding wing-like from the fore part of the 
body. They have no disk to walk upon, nor arms for the 
seizure of prey, like the cephalopods and gasteropods, but re- 
semble them by the possession of a head distinct from the rest 
of the body, which some, like the Hyaleas and Cleodora’‘, con- 
ceal in a thin transparent or translucent shell, in which they 
also hide their head and wings at the approach of danger, and 
immediately sink to the bottom ; while others, like the blue and 
violet Clios, beautifully variegated with light 
red spots, are perfectly naked. They ge- 
nerally inhabit the high seas, and are but 
rarely drifted by storms or currents into the 
neighbourhood of the land. They mostly 
Hyalea globuiosa, SWim about freely, but sometimes also they 
are found clinging by their wings to floating 
sea-weeds. They are small creatures, but propagate so fast that 
the Clio borealis and Limacina arctica form the chief food of 
the colossal whale. 
While these two little pteropods, in spite of their minute pro- 
portions, deserve to rank among the most important inhabitants 
of the northern seas, the Mediterranean species belong mainly 
to the genera Hyalea, Cleodora, and Criseis—forms wholly 
unknown to our own fauna except as waifs. Vast shoals of 
these animals frequent the deeper parts of that sea, leaving 
their remains strewed over its bed, between depths of from 
one hundred to two hundred fathoms; they are short-lived 
creatures, and have their seasons, being met with near the 
