ORDER AMPHIPODA — GAMMARUS. 37 



GENUS GAMMARUS. Fabricius. 



Antennae with the last joint composed of numerous minute ones ; upper antennae as long or 

 longer than the lower, with four articulations, the last ending in a bristle ; lower antennae 

 with five articulations. Feet fourteen ; the two anterior pair monodactyle, subequal ; the 

 two following pair terminate in a simple curved nail. Tail with small fasciculate spines 

 above, and bifid ones at the tip. 



Gammarus MINUS. 



PLATE IX. FIG. 29. 

 Gammar its minus. Say, Jour. Acad. Nat. Sciences, Vol. 1, p. 376. 



Description. Body incurved, subcompressed. Upper antennae longest, with the setae short, 

 attaining the tip of the second articulation of the terminal joint, which has about twelve arti- 

 culations. Eyes reniform. 



Color. Body whitish, with a few pale fulvous spots on the sides. In dried specimens, the 

 color becomes reddish, and the lateral spots, more particularly towards the tail, are bright 

 red. 



Length, 0-15-0-3. 



This species is common in most of our fresh-water streams, and may often be detected 

 under stones and pieces of wood. It is extremely active, and is popularly known under the 

 name of Fresh-water Shrimp. 



(EXTRA-LIMITAL.) 



G. mucronatus. (Say, loc. cit. p. 376.) Antenna? subequal. Eighth, ninth and tenth segments of the 

 body mucronate above, more distinctly on the female. Length, 0*4. This and the succeeding 

 will in all probability be found in this State. Inhabits the coast from New-Jersey to Florida. 



G.fasciatus. (Id. lb. p. 374.) Eyes at the outer base of the antennae, reniform; terminal joint of the 

 upper antennae with about thirty articulations. Color, whitish, fasciate with faint green which 

 becomes reddish after death. Length, 0-4. Freshwater. Pennsylvania. 



G. locusta. (Montagu, Lin. Tr. Vol. 9, p. 359, pi. 4, fig. 1. Gould, loc. cit.) Eyes linear, almost 

 lunulated ; antennae covered with hairs ; threads of the caudal appendices subequal. Allied to the 

 preceding. Massachusetts. 



G. appendiculatus. (Say, 1. c. p. 377.) Caudal segments, and three terminal segments of the body, 

 dentated on their posterior edges. Feet in one sex with the second pair didactyle. Length, 0-3. 

 Georgia. 



