Osten Sacken.J 152 [October 6, 



femora black at base; tibia? with a trace of a brownish ring; tarsi 

 brownish. The abdominal crossbands usually reach the lateral mar- 

 gins of the segments, but quite often they stop a little distance be- 

 fore, leaving a narrow black border between; their color is reddish, 

 or pure yellow, with a more or less distinct whitish pollen, which 

 often gives them a whitish appearance. Length, 8-9 mm. 



Male. The face often, not always, has a more distinct metallic 

 bluish reflection ; the oral border is more often bordered with brown 

 here than in the female; the ground color of the abdomen is more 

 opaque. 



I compared twenty-five males and sixty-five females, mostly taken 

 by Mr. Morrison in the White Mountains, N. H. 



S. geniculatus Macquart, 1. c. 1 



Differs from my S. umbe/lalarum in being a little smaller (about 

 7.5 mm.); the face, in the profile, is much more projecting; the fa- 

 cial tubercle is metallic blackish green, which color extends on both 

 sides along the oral border; in the other species the facial tubercle 

 bears a distinct stripe; in the female the sides of the face, powdered 

 with yellow pollen, have a brownish yellow ground color; in the 

 male, the ground color seems to be blackish green throughout, al- 

 though mostly concealed under a thick covering of brownish yellow 

 pollen ; the antennae are inserted on black ground; the front, in the 

 female, is brownish green (not bluish green), it is much broader 

 than in the other species ; the pollen on the front is much less thick; 

 it follows on both sides the orbit of the eye to about half the dis- 

 tance between the ocelli and the antenna?, and does not reach as 

 much towards the vertex as in the other species; it does not form a 

 well defined arch; the glabrous space above the antenna? is smaller. 

 The thorax is brownish green (not bluish green); the scutellum has 

 a stronger bluish metallic reflection; the yellow markings on the 

 abdomen are somewhat narrower, and paler yellow; in other respects 

 they are exactly the same; the four anterior legs are of a darker red- 

 dish brown, sometimes almost black, with paler knees; when the 

 legs are paler, the base of the femora does not appear abruptly 

 tinged with black, as in the other species; hind legs black. 



The easiest character for the distinction of the two species at first 



1 1 became aware of the existence of this second species only after the beginning 

 of the present paper had been already put in type ; hence it is not mentioned in 

 my introduction, where S. umbellatarum and S. geniculatus are treated as prob- 

 able synonyms. 



