292 MARINE INVERTEBRATES 
habit ponds and streams of fresh water, and still others are found 
along the shores of all oceans, abounding among the marine vege- 
tation of the shallow waters. Some swim free in the open sea; 
others are brought up from the greatest depths. Others, again, 
are parasites, and live in the internal organs of fishes and prawns. 
Sometimes a prawn is found having what appears like a very 
swollen throat, which actually is a little parasitic isopod of the 
family Bopyride attached to its gills. 
Genus Cirolana 
C. concharum. The body consists of fourteen segments, the first 
being the head, the next seven the thorax, and the last six the abdomen. 
On the head are the triangular eyes, the antennules, and 
the antenna, and underneath is the mouth, which is 
covered by the maxillipeds. The dorsal surface is more 
or less rounded. At the bases of a]l the segmental thoracic 
rings excepting the first one are sutures marking off square, 
seale-like pieces (epimera). The epimera form a border 
tothe side margins. The legs are attached to the epimera, 
which are, in fact, the upper segments of the legs. The 
first three pairs of legs have a general resemblance to one 
another, and are directed forward. The last four pairs are 
much longer and flatter, and are directed backward. The 
telson, or last segment, is triangular, and the square or 
blunt apex is fringed with hairs. On the ventral surface 
of the thorax in the adult females there is a long pouch 
ek for the reception and development of the eggs. This spe- 
cies is usually about one and a half inches in length, but sometimes is 
longer. Its color is yellowish, with a brown edge on the posterior margins 
of the segments, somewhat translucent in the thinner parts. It is found 
from Cape Cod to South Carolina, swimming about in 
shallow water, and is especially abundant in winter. 
Genus Limnoria 
L. lignorum, the gribble. This little isopod is very 
destructive in its habits, boring into submerged wood- 
work, like the ship-worm (Teredo), and doing great 
damage to the piles of wharves, ete. It burrows to the 
depth of half an inch, and completely honeyeombs the 
surface of the wood, which then scales off or rapidly 
decays, and is washed away by the waves. The animal 
then begins anew, and in a short time, or at the rate of Zmnoria tignorum, 
about an inch a year, piles diminish in diameter where Mss icinagaad 
Limnoria is plentiful, and are finally destroyed unless protected from 
these little crustaceans by a sheathing of metal. Although considered 
as pests, they have an economic value not so often recognized, as they 
attack all driftwood, and in time entirely destroy floating and water- 
