126 THE ATLANTIC. (CHAP. II. 
ent parts of the body show iridescent blues and greens. Maulti- 
tudes of these little things may now and then be seen on the 
surface of the water, fluttering with their wings and glittering 
in the sunshine; to be compared with nothing more aptly than 
with a congregation of the more dressy of the bombyx moths, 
as one sometimes comes upon them on a sunny morning just 
after a family of them have escaped from their chrysalides. 
The Pteropods are much smaller than the larger forms 
among the Heteropods: the largest of the present day are not 
more than about an inch in length, though antediluvian spe- 
cies of the genus Conularia and its allies sometimes reached a 
length of nearly two feet. They make up for their small size, 
however, by their numbers. Everywhere in the high seas they 
absolutely swarm. They are not always to be taken in the tow- 
ing-net, as they seem to have a habit,in the heat of the day and 
when there is any wind, of swimming a little way below the 
surface; but in a fine calm evening, no matter where, a haul of 
the towing-net can scarcely be made without catching many 
of them. 
The most widely distributed species in the Atlantic seems to 
be Diacria trispinosa, with a little pocket-like shell of some 
weight and strength, shaded purple and 
white. Several species of Cavolinia are 
abundant, the largest C. tridentata. Clio 
cuspidata, with a fretted shell whose orna- 
ment reminds one of some of the fossil 
genera, is perhaps the species most frequent- 
ly seen on the surface, and the one which 
shows the iridescent coloring with the great- 
est brilliancy (Fig. 25). The several species 
of Styliola, much smaller than the others, 
are much more numerous, and sometimes 
Fic. 25.—Clio pyramidata, throng the towing-net with their glassy 
Browne. Slightly en- iG 
larged. Surface. (No.4.) Needles. Styliola subulata, S. actcula, and 
