1875.] 143 [Osten Sacken. 



Observation II. It is the place here to mention two American spe- 

 cies, described by previous authors, and compared by them to the 

 European S. ribesii. 



In comparing his Scceva concava with that species, Say must have 

 had a female of the former, and a male of the latter, before him. 

 Thus the distinction he establishes, " crossbands concave " in the 

 American species, and " acutely notched " in the European, is a 

 merely sexual difference, and not conclusive. The words "feet whit- 

 ish, dull rufous at base," " head whitish cinereous, antennae pale 

 testaceous," do not agree with any Syrphus known to me. 



Macquart's S. philadelpMcus (Dipt. Exot., n, p. 93. a male) must 

 be either & rectus or S. tor&us, it is difficult to decide which, as Mac- 

 quart does not say whether the eyes are pubescent or not. It will 

 perhaps be better to cancel for the present these two insufficient 

 descriptions. 



3. S. Lesueurii. 



Syrplms Lesueurii Macquart, Dipt. Exot., n, 2, p. 93.; female. 



Epistrophe conjungens Walker, Dipt. Saunders., p. 242, Tab. VI, 

 f. 5; male. 



Will be easily recognized by Westwood's excellent figure of the 

 male in the Diptera Saundersiana. Larger than S. topiarius, and 

 with a much narrower abdomen.; in the female the abdomen is a little 

 broader, still less broad than in the allied species. The yellow face 

 has a brown, abbreviated stripe in the middle (sometimes wanting); 

 the antennae are uniformly black. Eyes bare. The yellow spots and 

 crossbands on the abdomen are straight, and reach the sides of the 

 abdomen with their full breadth; the yellow has a bluish reflection 

 (seldom indistinct); in the male the band en third segment has a 

 sharp triangular notch in the middle of the hind margin, which does 

 not exist in the female; the fourth and fifth segments often have a 

 greenish reflection, and are margined with yellow posteriorly. The 

 femora are black at the base, the hind tibiae have a distinct brown 

 ring. The wings usually have a distinct yellowish tinge. 



Length 12-13.05 mm.; some rare specimens of both sexes are only 

 8 mm. long. 



I compared about ninety male and female specimens, principally 

 from the White Mountains (collected chiefly by Mr. Morrison) ; also 

 from Maine, Massachusetts, Saratoga, N. Y., etc. 



Macquart calls the thorax black, but so he does the thorax of his 



