122 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 113 
Fort Sherman, April 20, 1925, O. F. Cook; Frijoles, July 13, 1923, 
H. F. Loomis; Monte Lirio, June 8, 1923, O. F. Cook. Panama, 
many specimens from following localities: Alahjuela, July 20, 1923, 
H. F. Loomis; El Valle, March 22, 1958, E. M. and H. F. Loomis; 
Juan Dias, June 3, 1923, O. F. Cook and H. F. Loomis. All paratypes 
in author’s collection. 
Diagnosis: Related to S. progressor Chamberlin but differing in 
shape and proportions of head and beak as well as in features of the 
gonopods. 
Description: Body parallel-sided except for two or three segments 
at each end, where it narrows abruptly; extremely variable in length 
and number of segments, mature males ranging from 20 to 40 mm. 
long and 1 to 1.2 mm. wide, with 75 to 145 (type) segments; females 
20 to 64 mm. long and 1.1 to 1.3 mm. wide, with 75 to 170 segments; 
color in life grayish white becoming yellowish in alcohol; dorsum not 
strongly convex, the keels fairly conspicuous and slightly raised above 
the adjacent dorsal surface so that in cross section the dorsal outline is 
triarcuate, none of the keels caudally produced; sides below pores 
nearly flat, scarcely convex, descending vertically or obliquely inward; 
dorsum rather sparsely covered with short erect hairs through which 
the shining surface is seen easily. 
Head triangular, considerably exceeded in length by the nearly 
straight beak, which reaches to end of antennal joint 5 (fig. 8g-h); 
antennae with joint 2 as long or longer than any other joint, very 
strongly clavate, its base narrower than any other joint and much 
less setose, the suddenly widened apical portion as wide as or wider 
than any other joint; joint 6 narrower than preceding ones; hypostomal 
plate well exposed, wide, the apex squarely truncate (fig. 87), sides 
diverging caudally; mentum narrow at base, sides slightly convex. 
Segment 1 wider, shorter, less deeply emarginate in front, and with 
each side more divergent caudally than in S. progressor; outer side 
of segment descending almost vertically to the free edge, which is 
not curved under body, is nearly straight and twice as long as the 
edge of segment 2. 
First and second legs of both sexes stouter than any that follow; 
first pair with anterior face of each coxa produced into a rather long 
narrow lobe exposed over the hypostomal plate. 
Anterior and posterior gonopods shown in figure 82-7. 
