ORDER ISOPODA — FLUVICOLA. 53 
exclusively fossil genera known under the name of Trilobites. It is here also that I venture 
to place a curious crustacean, which I find no where described. In my original notes I find 
it arranged under the order Peczlopoda, but I prefer placing it provisionally at the end of this 
order. 
GENUS FLUVICOLA. 
Body elliptical or oval, slightly narrowed behind. Antenne four, all concealed beneath the 
buckler ; the outer curved and longest, of three articulations ; the two posterior straight, 
and scarcely half the length of the others. Segments of the body trilobate. Feet three 
pair. Fluviatile. 
FLuvicoLa HERRICKI. 
PLATE X FIG.37. FIG. 38 & 39, MAGNIFIED. 
(STATE COLLECTION.) 
Description. Body ovate-elliptical, membranous and flexible, consisting of twelve segments 
vaulted in the center, and becoming thin and translucent on the edges ; its whole disk mar- 
gined with subequal closely approximated hairs. The head or anterior segment with faint 
sutures, dividing it into three pieces ; near its junction with the first segment of the body is a 
dark colored spot, which, under the lens, presents a tubercular appearance. The two follow- 
ing segments are broader than the eight succeeding ones, and all, except the last, are divided 
by two longitudinal fissures into three series of lobes, giving to the animal a striking resem- 
blance to trilobites. The edges of the central plates, where they touch each other, are consi- 
derably elevated ; the lateral plates free, and admit of motion over each other. The whole 
upper surface is irregularly marked with serpentine lines and small round spots. Beneath, 
the mouth appears under the junction of the anterior segment with the following, resembling 
a short sac or tube with a transverse opening; and on each side, two dark processes, appa- 
rently the rudiments of jaws. Antenne four; the two anterior longest, curved, not reaching 
the outer margin of the buckler; the two inferior straight. Immediately posterior to the 
mouth arise three pair of unguiculated feet, of which the posterior pair is shortest ; they are 
furnished with scattering rigid hairs, and with a single black hook at the tip. Posterior to 
these feet are five pair of branchiopodal processes, resembling bunches of white tendinous 
filaments. Under a powerful lens, a dorsal vessel may be traced on each side, communi- 
cating with each tuft of filaments. Each tuft appears divisible into two, and these again are 
composed of seven or eight single filaments. Color, greyish brown. 
Length, 0°2-0°3. 
