SUBTERRANEAN AMPHIPOD STYGONECTES 53 



Diagnosis. — Closely allied with S. pizzinii but distinguished from 

 that species by the less elongate 1st gnathopod and telson and by 

 having fewer lateral spines on the telson in both sexes, and specifi- 

 cally in mature males by the more prominent distal notch in palmar 

 margin of 1st gnathopod, ventrally produced distoposterior lobes of 

 7th pereopod basis, and by the broader and more setose 4th segment 

 of pereopod 6. Largest males, 9.75 mm; largest females, 8.25 mm. 



Male. — Antenna 1 about 25 percent longer than antenna 2, about 

 50 percent as long as body; primary flagellum with up to 22 segments. 

 Antenna 2, flagellum with up to 12 segments. Mouth parts corre- 

 sponding to those described for the pizzinii group. 



Gnathopod 1: propod palmar margin relatively straight, oblique, 

 armed with a double row of 7 or 8 spine teeth and with a weU-defined 

 notch distally near the angle formed with the dactyl base; posterior 

 angle with 2 large and 5 small spines on outside, 5 small spines on 

 inside; posterior margin with 4 sets of setae; lateral setae few in 

 number, singly inserted; dactyl claw short. Gnathopod 2: propod 

 palmar margin generally straight, less oblique than in gnathopod 1, 

 armed with a double row of about 6 small spine teeth; posterior 

 angle with 2 large and 4 small spines outside, about 7 small spines 

 on inside; posterior margin with 6 or 7 sets of setae; lateral setae 

 in transverse rows, singly inserted; claw of dactyl long; coxal plate 

 with about 5 setae and 1 spinule marginally. Coxal plates of pereo- 

 pods 3 and 4 with 7 or 8 marginal setae each. Pereopod 6: segment 

 4 broadly expanded posteriorly, up to 75 percent as broad as corre- 

 sponding basis, with about 15 setae and 4 spines on posterior margin. 

 Pereopod 7: basis nearly as long as combined lengths of segments 

 3, 4, and 5, with 2 ventrally produced distal lobes extending beyond 

 segment 2 and with the posterior lobe just overlapping the anterior 

 lobe distally. Gill arrangement complete. 



Abdominal side plates corresponding to those described for the 

 pizzinii group. Pleopod 1, peduncle with 4 or 5 lateral setae on 

 outer margin. Uropods 1 and 2 as noted for the pizzinii group 

 and as shown m figure 11. Uropod 3, ramus about 50 percent as 

 long as peduncle, armed apically with 2 long spines and 1 short spine. 

 Telson approximately 50 percent longer than broad, lateral margins 

 with 1 or 2 spines each, apex convex and armed with 8 unequal spines. 



Female. — Differing from the male as follows: Antenna 1, primary 

 flagellum with up to 19 segments. Antenna 2, flagellum with 11 

 segments. Gnathopod 1: propod palmar margin straight, obhque, 

 armed with a double row of 7 or 8 small spine teeth; posterior angle 

 with 2 large and 2 small spines on outside, 3 small spines on inside; 

 posterior margin with 3 sets of setae; claw of dactyl long. Gnatho- 

 pod 2 about like that of male but with a few less spines on posterior 



