78 BULLETIN 31, UNITED STATES NATIONAL MUSEUM. 



Female. Very like tbe female of S. torvus ; the differences, as given 

 above, consist in the entirely glabrous eyes and the femora, which are 

 yellow from the very base (coxse black); in most specimens the hind 

 femora have a brown ring before the tip. 



The size, as well as the shape, of the abdominal stripes are very varia- 

 ble (the female of ;S^. torvus shows, in both respects, much less variation). 

 Between the following two extremes all intermediate stages occur. 



(1) The smallest specimens, from 7™™ upwards in length, have the 

 yellow stripes on the third and fourth segments quite straight, not at- 

 tenuated before coming in contact with the lateral margin ; their hind 

 borders show no perceptible conv«xity or concavity ; such specimens 

 usually have a distinct brown ring on the hind femora, a little before 

 the tip. 



(2) Larger specimens, up to 11 to 12™°> long, have the stripes on the 

 third and fourth segments, with a distinctly biconvex hind margin, with 

 a sinus in the middle; these stripes are distinctly attenuated on each 

 side, before reaching the lateral margin. Such large specimens often 

 have no brown ring on the hind femora. 



Male. Differs from the female in the femora being black at base; 

 the four anterior ones for about one-third of their length ; the hind ones 

 altogether black or brown, except at the tip. The majority of the speci- 

 mens before me are of medium size (about 8 to lO'"™)- ^^"t some larger 

 ones also occur. The shape of the yellow bands does not vary as much as 

 in the female ; they are always attenuated at both ends and biconvex 

 posteriorly, with a sinus in the middle. The altogether glabrous eyes 

 easily distinguish S. ribesii i, from 8. torvus $ ; in other respects they 

 look very much alike. The average size of 8. ribesii <? , is a little smaller. 



Minor differences between *S'. torrns and S. ribesii, available for both 

 sexes, are: 



(1) The face under the eyes is altogether yellow here ; there is no gray- 

 ish spot, as is always visible in S. torvus. 



(2) The sides of the face in S. torvus are beset with very distinct black- 

 ish pile; in 8. ribesii this pile is of a pale color, and almost impercepti- 

 ble ; hence the face looks smoother. 



(3) The antenna are less dark, more reddish in S. ribesii. 



(4) The scutellum is of a slightly purer yellow. 



(5) The four anterior tibise are less brown, more reddish, especially 

 on the first joint. 



(G) The contact of the abdominal yellow spots and bands with the 

 lateral margins is slightly broader in S. ribesii; hence the yellow pro- 

 longation or neck of the spots on the second segment is broader, and, 

 consequently, seems to be shorter. 



(7) The stigma of the wings is much paler, yellow rather than brown. 



(8) The metallic green thorax is somewhat more shining, less dull 

 than in ;S^. torvus ; in many specimens, however, this difference is scarcely 

 perceptible." — Osten Sacken, 1. c. 



