A NEW FRESH- WATER CRUSTACEAN. 29 



ing, white, mottled with brown. Palmar margin of hand 

 strongly angulate near the base, the angle preceded by 

 about five short spines. Between the angle and the dac- 

 tyl is a large, sharp tooth-like projection. Dactyl with 

 minute appressed spines on the inner edge, terminating in 

 a small claw. First genital plates of male with the quad- 

 rate basal segment about equal in length to the greatest 

 width of the lance-shaped distal segment. Second pair of 

 genital plates of male with proximal segments about as 

 wide as long ; distal segment of outer ramus fringed with 

 long hairs, obliquely truncate. Caudal appendages of 

 adults rather large ; the pedicel slightly excavate at middle 

 of its inner margin, about two and a half times as long as 

 wide ; outer ramus about three-fourths the length of the 

 inner ramus. 



Length of adult males .63 inch; width .25 inch; lower 

 antennae, .38 inch. Length of adult females .44 inch. 



A large and abundant crustacean in springs and spring- 

 fed rivulets and ponds in eastern Kentucky. Large ex- 

 amples are of a dull gray color with the expanded lateral 

 portions of the head and body- segments paler. In young 

 the contrast between the central and lateral portions of 

 segments is more decided, and two longitudinal dusky 

 bands appear on each side, one just outside of the median 

 ridge, and the other just within the expanded lateral por- 

 tions of the segments. 



The species is closely related to the Virginian Manca- 

 sellus brachyurus, but may be distinguished at once by the 

 fissured lateral portion of the head, and by the greater 

 length and different shape of the caudal appendages. Other 

 differences equally important with these become appar- 

 ent under the microscope, as will be seen by comparing the 

 accompanying figures. 



