SUBTERRANEAN AMPHIPOD STYGONECTES 99 



Pereopod 7 between 40 and 55 percent as long as body, a little longer 

 than pereopod 6 and about 30 percent longer than pereopod 5; seg- 

 ment 6 with 3 or 4 (occasionally 2) sets of spines on posterior margin. 

 Bases of pereopods 5-7 : posterior margins of 5 and 6 nearly straight, 

 that of 7 convex; distoposterior lobes rather broad. Dactyls of 

 pereopods 6 and 7 about 1/4 as long as corresponding propods, that of 

 pereopod 5 about 1/3 as long as corresponding propod. Median 

 sternal, pleonite sternal and 7th pereopodal coxal gills absent; lateral 

 sternal gills simple. 



Abdominal side plates: posterior margins gently rounded, with 4 

 to 6 setae each; posterior corners rounded; ventral margin of plate 2 

 with 2 to 4 spines, that of plate 3 with 3 to 5 spines. Pleopod 1, 

 inner ramus 20 to 30 percent longer than peduncle. Uropod 1 : outer 

 ramus about 80 percent as long as inner ramus, about 50 percent as 

 long as peduncle, with 8 spines; inner ramus armed with 7 or 8 spines; 

 peduncle with about 10 spines. Uropod 2: outer ramus 65 to 70 

 percent as long as inner ramus, 50 to 60 percent as long as peduncle, 

 armed with 5 or 6 spines; inner ramus with 8 or 9 spines; peduncle with 

 5 spines. Uropod 3, ramus 50 to 60 percent as long as peduncle, 

 armed apically with 2 or 3 spines. Telson about as long as broad, 

 sometimes a little longer than broad, a little broader proximally than 

 distally; convex apex armed with 8 to 11 spines (usually 11). 



Male. — Differing from the female principally in structure and larger 

 size of gnathopodal propods and to a lesser extent in structure of the 

 telson. Gnathopod 1 : propod palmar margin straight to slightly 

 convex, armed with a double row of 10 or 11 larger spine teeth; 

 posterior angle with 1 large spine and 3 to 5 smaller spines on outside, 

 3 to 6 small spines on inside ; posterior margin with 3 or 4 sets of setae ; 

 lateral setae fewer in number, singly inserted ; dactyl claw rather long. 

 Gnathopod 2: propod palmar margin straight, armed with a double 

 row of 10 or 11 larger spine teeth; posterior angle with 1 large spine 

 and 3 or 4 smaller spines on outside, 3 or 4 small spines on inside; 

 posterior margin with 4 sets of setae; lateral setae fewer, in transverse 

 rows, mostly singly inserted; dactyl claw rather long. Uropod 3, 

 ramus sometimes a little shorter in proportion to peduncle. Telson 

 about 20 percent longer than broad, a little broader proximally than 

 distally; convex apex armed with 8 to 11 unequal spines, the outer 

 spine on either side deflected laterally from the midline and sometimes 

 possessing 1 small, distal tine. 



Variation. — Major variation was observed in the ratio of length 

 of antenna 1 to length of body (table 5), in the number of posterior 

 angle spines of gnathoj^odal propods, in the coxal plates of pereopods 

 2, 3, and 4, in the ratio of length of seventh pereopod to length of body, 

 and in the number of apical spines on the ramus of the third uropod. 



