46 BULLETIN 31, UNITED STATES NATIONAL MUSEUM. 



pallid ou each side ; tubercle rather large, obtuse. Dorsum of thorax 

 and scutellum roughened ; abdomen very lightly punctulate, shining. 

 Legs lutescent; femora, except the tip, black; hind tibia? and metatarsi 

 subfuscous, lutescent at base and tip. Halteres whitish; tegulse white. 

 Wings subhyaline, lightly cinereous sublutescent, base clearer, stigma 

 more saturate lutescent.— Translation. 



ADDITIONAL NORTH AMERICAN SPECIES. 

 Chilosia frontosa Bigot, Ann. Soc. Ent. de Fr., 18ft'4, obo (Cartoayrphus).— Mexico. 



MELANOSTOMA. 



Melanostoma Scbiuer, Wien. Eutouj. Monatscbr., iv, 213, 18C0. 



Medium size, exceptionally large, species, thinly pilose or nearly 

 bare, metallic black or black green ; the abdomen with lighter- colored, 

 spots or bands, usually slender. Head hemispherical. Antenna^ short; 

 third joint oval or a little elongate ; arista basal, bare. Face distinctly 

 tuberculate, nearly bare, always black or black-green, never in ground 

 color yellow, though frequently with whitish dust. Eyes bare, contig- 

 uous in the male. Thorax shining, never with yellow or reddish mark- 

 ings. Abdomen elongate, slender, rarely niuch oval, considerably flat- 

 tened. Legs simple, the hind metatarsi sometimes a little thickened. 

 Wings rather large, extending beyond the abdomen ; marginal cell open ; 

 third vein nearly straight; outer anterior angle of iirst posterior cell 

 acute. 



TABLE OF SPECIES. 



1.— Legs red, not very slender, the hind metatarsi a little thickened; third abdominal 

 segment scarcely at all narrowed behind ; second, third, and fourth segments 

 with metallic cross-bands, the last not interrupted; wings only a little longer 



than the abdomen rufipes. 



Legs more or less black ; or, if without black, slender, and the hind metatarsi not 



at all thickened 2 



2.— Legs quite slender, the metatarsi of the male not thickened, abdomen in the male 



with three pairs of reddish-yellow spots 3 



Hind metatarsi of the male always somewhat thickened ; bands of abdomen me- 

 tallic or greenish, not reddish-yellow 4 



3. —Face with a prominent tubercle; abdomen of male narrow, elongate, broadest at 



tip of fourth segment, spots elongate angustatum. 



Tubercle of face not at all prominent, indistinct; abdomen not elongate, not broad- 

 est at tip of fourth segment, spots quadrate; in female oval with four pairs 



of triangular spots mellinum. 



4.— The pollen of the face leaves small circular confluent spots, ripple-like, of the 

 ground color; second abdominal segment distinctly broader behind, 



tigrinum. 

 The pollen of the face is uniform, or if somewhat ripple-like, not composed of cir- 

 cular spots , 5 



5.— Pollen of face somewhat striate on the sides; pile of thorax dusky . obscurum. 



Pollen of face uniform; pile of thorax whitish 6 



6.— Abdomen slender ccerulescens. 



Abdomen oval {Sijrx)hn8 simplex). 



For additional species, see descriptions. 



