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 Pcecilopoda, but I prefer placing it provisionally at the end of this 

 order. 



GENUS FLUVICOLA. 



Body elliptical or oval, slightly narrowed behind. Antennae 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 lube with a transverse opening ; and on each side, two dark processes, appa- 

 rently the rudiments of jaws. Antennae 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. 



