264 NORTH AMERICAN DIPTERA 



92. Epistoma produced into a long, porrect snout Lycastrirrhyncha Bigot 



Epistoma not pi'oduced 93 



93. Eyes light brown with numerous small brown spots. 



Lathyrophthalmus Mik 

 Eyes normally unicolorous 94 



94. Thorax with yellow markings of short, squamose hairs (140, 142). 



Meromacrus Rondani 

 Hair of the thorax never squamose or forming dense yellow patches 

 (17, 143 ) *Eristalis Latreille 



95. Posterior femora before the apex with a strongly raised, sub-triangular 



ridge, the base with a distinct spur Merodon Meigen 



Posterior femora variable, but never with a spur bearing triangular 

 plate or strong ridge 96 



96. Eyes pilose 97 



Eyes bare 98 



97. Third antennal segment not longer than wide (141, 147).tMallota Meigen 

 Third antennal segment twice as long as wide Quicbuana Knab 



98. Mesonotum densely and evenly yellow pollinose, the ground color con- 



cealed; face concave in female; with a tubercle bvit receding below 



in the male ( 138 ) Pterallastes Loew 



Mesonotum differently colored 99 



99. Large robust species, the thorax thickly yellow or orange pilose, 



rarely whitish; posterior femora swollen and arcuate in both sexes; 



rather bumble-bee-like flies (141, 147) fMallota Meigen 



Usually smaller and always more slender; if the posterior femora are 

 arcuate the tibise end in an apical spur 100 



100. Posterior tibite ending in a spur or triangular production, never 



transverse on the ventral apex 101 



Posterior tibise transverse or rounded apically, never produced 102 



101. Large species, at least 12 mm. in length, the mesonotum at most 



obscurely vittate (34, 145, 148) Polydontomyia Williston 



Smaller, more slender species, the mesonotum usually with two or 

 more cinereous or yellowish vitse (151) JLejops Rondani 



102. Face entirely pollinose (146) JParhelophilus Girschner 



Face with a shining median vitta on at least the lower half 103 



103. Stigma simulating a crossvein 104 



Stigma at least twice as long as wide, although often paler apically, 



never simulating a crossvein (18) JElophilus Meigen 



104. Ocellar triangle extremely large in both sexes, the outer ocelli lying 



very close to the eyes (150) JAsemosyrphus Bigot 



Ocellar triangle smaller (149) tLunomyia Curran and Fluke 



* Cui-i-an, 1930, Anier. Mus. Novit. No. 411, p. 3. 



t Curran, 1930. Bull. Amer. Mus. Nat. Hist., Ixi. p. 74. 



t Curran and Fluke, 1926, Trans-Wisconsin Acad. Sci., Arts & Letters, xxii, pp. 207-2S1, 



