SUBTERRANEAN AMPHIPOD STYGONECTES 109 



little longer than pereopod 6 and about 35 to 40 percent longer than 

 pereopod 5. Pereopods 5-7 differmg from those of S. clantoni only 

 in the form of the bases, which are proportionately less broad and 

 possess smaller distoposterior lobes. Basis of pereopod 7 more narrow 

 than bases of pereopod 5 and 6. Sternal gills absent on 1st pleonite; 

 all other gills present. 



Abdominal side plates similar to S. clantoni but perhaps with a few 

 less setae. Pleopod 1, inner ramus about 30 percent longer than 

 peduncle. Uropod 1 : outer ramus about equal to inner ramus in 

 length, 60 to 65 percent as long as peduncle, armed with about 13 

 spines; inner ramus with about 11 spines; peduncle with about 18 

 spines. Uropod 2: outer ramus about 3/4 as long as inner ramus, 

 approximately 2/3 the length of peduncle, armed with about 9 spines; 

 inner ramus with 9 or 10 spines; peduncle with about 6 spines. Uro- 

 pod 3, ramus about 50 percent as long as peduncle, armed apically 

 with 2 or 3 spines. Telson more than twice as long as broad; armed 

 laterally with about 1 small spine per side ; weakly convex apex with 

 about 20 unequal spines. 



Female. — Differing from the male as follows: Antenna 1 up to 

 68 percent as long as body but usually varying between 55 and 65 

 percent, between 35 and 45 percent as long as antenna 2; primary 

 flagellum with up to 34 segments. Antenna 2, flagellum with 11 to 

 14 segments. Gnathopods differing only in a few details: 1 more 

 small spine on mside and outside of posterior angle, 3 marginal setae 

 on dactyl normally inserted, 4 sets of setae on posterior margin of 

 gnathopod 2. Uropod 1 : outer ramus about equal in length to inner 

 ramus, about 50 percent as long as peduncle; rami with about 12 

 spines each; peduncle with 14 spines. Uropod 2: outer ramus about 

 3/4 as long as inner ramus, about 50 percent as long as peduncle, 

 armed with about 7 spines; inner ramus with about 12 spines; peduncle 

 with 6 spines. Uropod 3, ramus about 1/3 as long as peduncle, armed 

 apically with 4 to 6 spines. Telson about 1/3 longer than broad, 

 armed dorsolaterally with 2 to 4 spines per side and apically with 19 

 or 20 unequal spines. 



Variation. — ^The unusual manner of setal insertion on the dactyls 

 of the gnathopods and flagellar segments of the second antenna noted 

 in the male has so far been unobserved in any other species of this 

 genus. The point of insertion appears to be a slightly depressed, 

 circular basin, the exact morphology of which is unknown. Especi- 

 ally among females, there appears to be slight inter- and intra-popula- 

 tion variation in the number of dorsolateral spines on the telson. 



Type locality. — Marvel Cave, Stone Co., Mo. This cave is one 

 of the largest and best known commercial caves in IVIissouri, and ac- 



