PTEKOPODA. 517 
which the Blackfoot Indian adorns the head of his horse, and the two 
tentacles placed more towards the front. In the skin are imbedded a vast 
number of little spicules. 
The beautiful EOLIs is common on our own coasts, and may be seen 
moving over the plants and stones with tolerable activity and always keeping 
the tentacles and papillze in motion, sometimes contracting and sometimes 
extending them, while the movement of the water causes them to wave in a 
very graceful manner. These papilla possess the property of discharging 
a milky kind of fluid when the animal is irritated. The fluid, however, is 
quite harmless, at all events to the human skin. As in the previous case, the 
papille are liable to fall off at a touch. 
A SMALL, but important, group of molluscs now comes before us. These 
are the Pteropoda, or Wing-footed Molluscs, so called from the fin-like lobes 
that project from the sides, and are evidently analogous to the similar organs 
in some of the sea-suails. These appendages are used almost like wings, 
the creature flapping its way vigorously through the water, just as a butterfly 
HYALEA.—(Hya/ra tridentata.) CLEODORA.—(Cleodora pyramidata.) 
(Empty shell below.) 
urges its devious course through the air. They are found in the hotter seas, 
swimming boldly in vast multitudes amid the wide waters, and one species 
(Clioborealis) has long been celebrated as furnishing the huge Greenland 
whale with the greater part of its subsistence. ‘ 
. The curious figure on the left hand of the illustration is the HYALEA, 
remarkable not only for the two wide fins which are found in all the family 
to which it belongs, but for the long appendages which pass through certain 
apertures in the shell, and trail behind as the creaturé proceeds on its course. 
It will be also seen that the wings are united by a nearly semicircular lobe. 
The empty shell is placed below in order to show its structure. . 
Just on the right of the Hyalea is a smaller creature, with an odd-looking 
three-pointed shell, hanging as it were from the wings. This is the 
CLEODORA, a very beautiful and interesting animal, of which Mr. F. D. 
