SUBTERRANEAN AMPHIPOD STYGONECTES 



105 



pereopod 5 proportionately longer, about 40 percent as long as 

 corresponding propod. Median sternal and pleonite sternal gills 

 absent. 



Abdominal side plates: posterior margins gently rounded, convex, 

 3 to 5 setae on 1st and 6 or 7 setae each on 2nd and 3rd; posterior 

 corners rounded; ventral margins of plates 2 and 3 with 4 or 5 spines 

 each. Pleopod 1, inner ramus about 30 percent longer than peduncle. 

 Uropod 1: outer ramus a little shorter than inner ramus, about 50 

 percent as long as peduncle, armed with about 10 spines; inner ramus 

 with about 14 spines- peduncle with about 18 spines. Uropod 2: outer 

 ramus about 2/3 as long as inner ramus, about 50 percent as long as 

 peduncle, armed with about 6 spines; inner ramus with about 12 

 spines; peduncle with up to 6 spines. Uropod 3, outer ramus about 

 1/3 as long as peduncle, armed with 2 or 3 spines apically. Telson 

 about 40 percent longer than broad, weakly convex apex armed with 

 24 or 25 rather short spines. 



Table 6. — Variation in the ratio of length of 1st antenna to length of body in two 

 populations of Stygonectes clantoni {Greaser) 



Variation. — A significant interpopulation difference in the ratio of 

 length of first antenna to length of body was noted between samples 

 (presumably of sexually mature animals) from Harrisonville, Mo., and 

 Purity Spring, Kans. (table 6). A t-test indicates difference be- 

 tween the means to be significant (2)<0.05). These two populations 

 are separated by several major rivers and a distance of 100 miles. 

 Further variation was observed in the number of apical spines on the 

 third uropod. Females from Purity Springs had three apical spines 

 on this appendage while those from other populations, including a 

 single female from nearby Rutherford Cave, had only two apical 

 spines. The only male, however, with more than two apical spines 

 on the third uropod was the holotype from Franklin Co., Kans., which 

 had three spines on one uropod but only two on the other. 



