96 OUR CARCINOLOGICAL FRIENDS. 
the beach-flea. Examine the legs of one of these 
animals, and you will observe that they are disposed 
on either side in two dissimilar series; hence the 
name of Amphipoda, double-footed, that has been 
applied to the broad group to which the hopper 
belongs. Two closely related, but larger, species, 
of a gray rather than of an olive or brown color, 
constitute the genius Talorchestia. 
A form much like the preceding, but with aquatic 
habits, is found in both salt and fresh waters, 
largely frequenting the meshes of the rock-weed 
(Fucus). The Gammarus (PI. 7, Fig. 5), for so the 
animal is known to naturalists, is a helpless creature 
out of water, shuffling along on its side in a vain 
endeavor to elude its pursuers or to regain the 
water. It occurs in vast numbers in favored lo- 
calities, contributing largely to the food-supply of 
many of our coast fishes. 
Another interesting amphipod of our coast is 
found abundantly on the surfaces of submarine 
plants, and also on sponges, where it may be seen 
moving about in the manner of the ordinary meas- 
uring-worms, arching over its body, and advancing 
alternately the two extremities. From this close 
resemblance to the progression of the geometer 
worms it has received the name of Caprella geo- 
metrica (P|. 7, Fig. 3): 
Of the less attractive group of the sow-bugs, 
many of whose members, such as the Bopyrus, 
already mentioned, are parasitic on the tissues of 
other animals, but few forms are likely to come 
to the notice of the visitor to the sands. One of 
