20 U.S. NATIONAL MUSEUM BULLETIN 2 59 



genus. The possible evolutionary significance of these groups is 

 discussed elsewhere in this paper. 



Key to Species Groups of Stygonectes 



1. Sexually mature males usually smaller than sexually mature females: 



gnathopod 1 often stouter but otherwise about equal to gnathopod 2 in 

 overall size (figs. 2r, s; 2Sn, o); pereopod 6 and 7 usually about equal in 



length 2 



Sexually mature males usually larger than sexually mature females; gnathopod 

 1 stouter and often somewhat larger than gnathopod 2 (figs. 11a, b; 12a, b; 

 18s, t) ; pereopod 7 a little longer than pereopod 6 excepting only one 

 poorly known species 5 



2. Posterior margin of 1st gnathopodal propod rather short, without setae 



except in one rare species (fig. 2r) ; posterior angle of 1st gnathopodal 

 propod with 2 to 6 large, unequal but typically curved spines on outside 

 (figs. 2r, 7m) ; posterior margins of abdominal side plates convex (figs. 



2o, Qh) 3 



Posterior margin of 1st gnathopodal propod with 3 to 5 groups of setae, 

 posterior angle with 1 large but usually straight spine on outside (figs. 2Sn, 

 29a) ; posterior margins of abdominal side plates weakly convex to relatively 

 straight (fig. 28g) 4 



3. Inner lobes of lower lip vestigial or absent (fig. 9t) ; distoposterior lobes of 



pereopod bases rather well defined (fig. 9c, d) ; posterior margins of abdom- 

 inal side plates with up to 10 setae (fig. 29j) ; telson without lateral spines, 



margin convex (fig. 29/i) spinatus group 



Inner lobes of lower lip not vestigial but sometimes small (figs. 2a, 4e) ; 

 distoposterior lobes of pereopod bases usually rather poorly defined or 

 nearly absent (figs. 2t-v; 7e-g); posterior margins of abdominal side plates 

 with up to 6 but more often fewer than 6 setae (figs. 2o, 7h, Sk) ; telson with 

 lateral spines and without shallow apical margin excavation (fig. 70, or 

 without lateral spines and with or without shallow excavation (figs. 3n, 6q) . 



emarginatus group 



4. Caxal plate of pereopod 4 large; bases of pereopods 5-7 broadly expanded 



posteriorly, distoposterior lobes broad and well defined; apical margin of 

 telson entire or with shallow excavation; telson without lateral spines. 



hadenoecus group 



Coxal plate of pereopod 4 normal, not enlarged (fig. 2Sg) ; bases of pereopods 



6-7 not greatly expanded posteriorly, distoposterior lobes rather small or 



poorly defined (fig. 28r-t) ; telson rather long, with or without lateral 



spines, apical margin without excavation (fig. 2Qj) , . . flagellatus group 



5. Propod of gnathopod 1 up to twice the size of propod of gnathopod 2, propod 



palmar margin of sexually mature males with a prominent distal notch or 

 shallow excavation (fig. 11a, b); basis of pereopod 7 of larger males with a 

 prominent ventrally produced distoanterior lobe (fig. Hi); telson with 



lateral spines (fig. llo, s) pizzinii group 



Propod of gnathopod 1 larger but not twice as large as propod of gnathopod 

 2, propod palmar margin of sexually mature males without distal notch or 

 excavation (figs. 12a, b; 25i, j); larger males without a prominent dis- 

 toanterior lobe on pereopod 7 (figs. ISh, 25c); telson with lateral spines in 

 only 2 species tenuis group 



