38 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxii. 



Telson emarginate, the emargination reaching to the middle or 

 nearl}^ to the base; each lobe furnished at the truncate tip with three 

 or four stout spines. 



Length 10 mm. 



This species has been collected at various places within Nickajack 

 Cav^e, Shellmound, Tennessee. 



The genus Niphargus^ to which this species has been assigned by 

 Hay, differs from Crangonyx in the telson, which in the latter genus 

 is entire and in the former divided, and in the third uropods, which in 

 Crangonyx are uniramous and in Nlphargus biramous with the outer 

 ramus biarticulate. It differs from Eucrangonyx^ in which genus it 

 has been placed by Stebbing, in the outer ramus of the third uropods, 

 which in Encrangonyx is uniarticulate and in Nij)hargiis biarticulate. 



Genus GAMMARUS Fabricius. 



KEY TO SPECIES. 



A. Telson cleft to the base. 

 B. Eyes present. 

 C. Third uropods with basal segment of outer ramus elongated, terminal segment 

 short, styliform; inner ramus half or more than half as long as the outer; 

 both rami furnished with long plumose hairs. 

 D. Inner ramus of third uropods at least three-fourths as long as the outer; 

 nearly as broad as the basal portion of the outer ramus. 

 PI Terminal segment of outer ramus of third uropods with long plumose 

 hairs on lateral margins; secondary flagellum composed of two to four 



segments G. limnxus, p. 42 



EE. Terminal segment of outer ramus of third uropods without long 

 plumose hairs on the lateral margins; secondary flagellum composed 



of five or six segments G.fasciatus, p. 40 



DD. Inner ramus of third uropods only slightly more than half as long as outer 



ramus; much more slender than the basal portion of the outer 



G. propinqims, p. 46 



CC. Third uropods with the basal segment of the outer ramus elongated, with 



fascicles of a few long hairs on lateral margins; terminal segment short; 



inner ramus rudimentary, shorter than the peduncle. . . G. ramellus, p. 38 



BB. Eyes absent G. accus, p. 47 



AA. Telson not cleft to the ))ase G. jmrpurascens, p. 45 



GAMMARUS RAMELLUS, new species. 



Eves small, reniform; their distance apart more than twice their 

 diameter. First antennae not quite half so long as the bod}^; first and 

 second segments of the peduncle about equal and nearly twice as long 

 as the third; flagellum composed of twent}' to twenty-five segments; 

 secondary flagellum slightly exceeding the terminal segment of the 

 peduncle in length and consisting of three or four segments. Second 

 antenniv more than half as long as the first pair; peduncle longer than 

 in the preceding pair; flagellum composed of eight to twelve segments. 



First gnathopods of the male with the carpus triangular, as broad as 

 long; propodus slightly longer than broad; lateral margins convex; 



