78 U.S. NATIONAL MUSEUM BULLETIN 259 



to that of gnathopod 1 ; posterior angle with several stout setae, 1 

 large spine and 4 smaller spines on outside, 4 small spines on inside; 

 posterior margin with 5 sets of setae; superior lateral setae doubly- 

 inserted, inferior lateral setae singly inserted; nail of dactyl long. 

 Coxal plates of pereopods 2 and 3 rather broadly rounded ante- 

 roventrally, about as broad as long, marginally with usually 6 or 7 

 setae. Coxal plate of pereopod 4 subquadrate, with about 7 setae on 

 ventral margin. Pereopod 7 about 45 to 50 percent as long as body, 

 a Httle longer than pereopod 6 and 40 to 50 percent longer than 

 pereopod 5. Dactyl of pereopod 5 approximately 1/3 as long as 

 corresponding propod; dactyls of pereopods 6 and 7 about 1/4 as long 

 as corresponding propods. Bases of pereopods 5-7 about as broad 

 proximally as distally; posterior margins gently rounded; distoposterior 

 lobes rather broad but not much produced ventrally. Sternal gills 

 sometimes absent on 1st pleonite; coxal gills rarely absent on 7th 

 pereopod; all other gills present. 



Abdominal side plates: posterior margins convex, with 4 or 5 setae 

 each; posterior corners rounded; ventral margins of plates 2 and 3 

 with 3 or 4 spines each. Pleopod 1 , inner ramus 40 percent longer than 

 peduncle. Uropod 1: inner and outer rami about equal in length, 

 about 60 percent as long as peduncle; rami and peduncle armed with 

 about 10 spines each. Uropod 2: outer ramus 1/2 to 2/3 as long as 

 inner ramus, about 1/2 as long as peduncle, armed with about 6 spines; 

 inner ramus with 10 spines; peduncle with 4 to 6 spines. Uropod 3, 

 ramus about 40 percent as long as peduncle and commonly armed 

 apically with 2 unequal spines. Telson a Uttle less than 50 percent 

 longer than broad, tapering distally; armed with 7 or 8 apical spines, 

 the outer ones on either side deflected laterally from the midUne and 

 armed with 2 or 3 inner, distal tines. 



Female. — Generally similar to the male but differing in a few details 

 as follows: Antenna 1 averaging about 50 percent longer than body 

 but varying between 37 and 68 percent; primary flagellum with 17 to 

 21 segments. Gnathopod 1: propod palmar margin less concave, 

 armed with an uneven, double row of 5 to 7 spine teeth; posterior 

 angle without a set of setae. Gnathopod 2: propod palmar margin 

 less concave, armed similarly but with smaller spine teeth; posterior 

 margin with 3 sets of setae; lateral setae long, singly and doubly in- 

 serted. Sternal gills present on pleonite 1 ; coxal gills rarely absent 

 on pereopod 7. Telson not much longer than broad, much less 

 tapered distally; armed apically with 8 undeflected and untined spines. 



Variation. — In about 50 percent of the populations for which 

 samples were available, males lacked sternal gills on the first pleonite, 

 but there did not appear to be a real geographic pattern to this varia- 

 tion. Samples from a cave and a seep in Laclede Co., Mo., and from 



