242 CHARLES W. J0IIN80N. 



terior margin, and only a small dorsal trianglu; fifth with a lateral margin, 

 widest anteriorly, and a dorsal line. In specimen referred to there is a round 

 spot on each side of the dorsal line ; venter yellow, with a central row of large 

 black maculations ; laterally attenuated along the anterior margin, but not reach- 

 ing the lateral or posterior edges : in some specimens the black on the second seg- 

 ment consists only of an irregular line ; the ventral markings are quite constant 

 in both sexes. 



9. — Face, front and occiput, yellow; oral margin, cheeks and medial facial 

 line (more or less distinct) a transverse line from the base of the antenute to the 

 eyes and the vertex, black ; in some specimens the two latter are narrowly con- 

 nected at the sides; vertical angle with two yellow spots, sometimes connected 

 on the cervex. Thorax black, with yellowish tomentuni ; scutellum wholly yel- 

 low. Abdomen black ; the variable yellow markings might be described from 

 three specimens, as follows: Firtit. — The square lateral markings on the second 

 seg)nent with a small lateral spot of ))lack ; the square lateral markings on the 

 third and fourth with a broad oblique incisure of black ; a small triangle on the 

 posterior margin of the second, a larger one on the third, and the one on the 

 fourth much larger and greatly attenuated, but not reaching the anterior margin ; 

 the yellow markings not connected at the posterior margin ; fifth with a dorsal 

 line, on the sides of whicli are .spots narrowly connected, but not connected with 

 the lateral margins. Secoiid. — The square lateral markings on the second segment 

 without the small black spots; lateral markings on the third and fourtli with 

 oblique black spots; second segment with a .small dorsal triangle, third with a 

 larger triangle; fourth with a much larger and attenuated triangle, not reaching 

 the anterior margin, the yellow markings connected at the posterior margin ; 

 fifth with a dorsal line, on each side of which is a spot narrowly connected with 

 the dorsal line and lateral margin. Third.— Th% square lateral markings on the 

 second segment with small black spots and a prominent dorsal triangle ; lateral 

 squares on the third with black spots and a larger dorsal triangle ; fourth segment 

 yellow, except a narrow anterior margin, the lateral spots and two minute point; 

 on the posterior margin of black ; the markings on the fifth segment might be 

 described as a broad dorsal line, with a spot on each side broadly connected with 

 the dorsal line and lateral mavgins, or yellow, with a narrow anterior margin, 

 and subtriangular markings at the posterior angles, of black. Femora black ; tips 

 of the femora, tibife and tarsi, reddish yellow ; middle of the tibise obscurely 

 annulated with brown, most prominent on the posterior tibite. Wings brownish, 

 veins dark yellow. 



Alameda County, California (Coquillett) ; San liafael County, 

 California, April and May (Osten .Sacken); Ogden, Utah (Riley), 

 U. S. National Museum. 



The above description is based on four males and four females. 

 The great variation in color is remarkable, in comparison with other 

 North American species. The black face and base of scutellum of 

 the male led Loew to describe it as another species. Baron Osten 

 Sacken, in Western Diptera, p. 218, refers to the two species S. 

 niaca/om and 'S'. Iii-'^igiiis as being identical. 



