82 U.S. NATIONAL MUSEUM BULLETIN 259 



Stygonectes montanus, new species 



Figure 19 



Synpleonia clantoni Greaser. — Hubricht and Mackin, 1940, p. 206 (in part). 

 Synpleonia americana (Mackin). — Hubricht, 1943, p. 711 (in part). 



Material examined 



ARKANSAS. — Polk Co. : Springs, Rich. Mt., Rich Mt. Station, male holotype, female 

 allotype, 18 paratypes, L. Hubricht, Apr. 26, 1936 (USNM and slide mounts of 2 

 paratypes in JRH). 



Diagnosis. — Distinguished from S. alabamensis, with which it is 

 apparently closely allied, by less concave and more spinose propod 

 palmar margins of gnathopods, 2 more spines on ramus of uropod 3 in 

 female, and by the telson which is more elongate and possesses more 

 apical spines. Largest males, 8.25 mm; largest females, 9.00 mm. 



Male. — Antenna 1 up to 70 or 75 percent as long as body and up to 

 60 percent longer than antenna 2; primary flagellum with up to 27 

 segments; accessory fiageUum reaching to about the end of 1st primary 

 flagellar segment. Antenna 2 with 10 segments in flagellum. Mouth 

 parts differing shghtly but not significantly from /S. alabamensis as 

 follows: Maxilla 2, inner plate with 7 long, obhquely placed, plumose 

 setae. Inner lobes of lower lip a little less broad. 



Gnathopod 1 : propod palmar margin shghtly concave, armed with 

 a double row of 8 or 9 spine teeth; posterior angle with 1 large spine 

 and 3 smaller spines on outside, 2 or 3 small spines on inside; posterior 

 margin with 4 sets of setae; lateral setae few in number, mostly singly 

 inserted; dactyl claw long. Gnathopod 2: propod palmar margin 

 shghtly concave, armed with a double row of about 8 spine teeth; 

 posterior angle with 1 large spine and 2 smaller spines on outside, 4 

 small spines on inside; posterior margin with 5 or 6 sets of setae; 

 lateral setae mostly doubly inserted; dactyl claw rather long. Coxal 

 plates of pereopods 2, 3, and 4 similar to S. alabamensis in relative 

 proportions but with 7,9, and 12 marginal setae, respectively. Pereo- 

 pod 7 between 50 and 55 percent as long as body, a Uttle longer than 

 pereopod 6, 35 to 40 percent longer than pereopod 5. Bases of 

 pereopods 5-7 similar to S. alabamensis; dactyls about 1/3 as long as 

 corresponding propods. Gill arrangement complete. 



Abdominal side plates: posterior margins convex, with 4 or 5 setae 

 each; posterior cornei-s rounded; ventral margins of plates 2 and 3 with 

 1 spine each. Pleopod 1, inner ramus approximately 40 to 45 percent 

 longer than peduncle. Uropod 1: outer ramus subequal to inner 

 ramus in length, about 60 percent as long as peduncle, armed with 10 

 spines; inner ramus with 9 or 10 spines; peduncle with 10 spines. 

 Uropod 2 : outer ramus about 75 percent as long as inner ramus, up to 

 2/3 as long as peduncle and armed with 7 spines; inner ramus with 9 or 



