166 CHARLES ROBERTSON. 



3. Front with two tubercles, one above the. other; mandibles 3-dentate; clypeus 



with a shining, somewhat concave, edge; vein a not before V 2 ; scopa 



white Dieeratosmia. 



Front without tubercles 4. 



4. Scopa yellowish; mandibles 4-dentate; vein a not before V 2 . 



Xanthosmia. 



Scopa black Osmia. 



Scopa white; mandibles 4-dentate 5. 



5. Vein a before V 2 ; clypeus rather strongly emarginate, with a rather dense 



apical fascia of dull whitish pubescence; front usually with an opaque 



blackish patch Monilosmia. 



Vein a not before V 2 6. 



6. Clypeus subquadrideutate, with a median emargination and two lateral teeth. 



Leucosmia. 



Clypeus entire; scopa sometimes blackish on segments 5-6 ; joint 5 of labial 



palpi minute Osmia. 



Males. 



Apical margin of segment 7 strongly bidentate 3. 



Apical margin of segment 7 entire or slightly emarginate, of 6 entire 1. 



1. Middle tarsi broad, three-sided ; joint 3 of antenna equals 4 ; hind metatarsi 



arcuate, clavate ; hind spur enormous, twice as long as its fellow spur. 



Centrosmia. 

 Middle tarsi simple 2. 



2. Intermediate femur produced beneath; antenna longer than thorax, joint 4 = 



2 + 3; hind metatarsus toothed beyond middle; pubescence mixed 



with black Oral osmia. 



Intermediate femur simple; joint 3 of antenna longer than 4; pubescence 

 pale ; small Leucosmia. 



3. Segment 6 entire medially, strongly sinuate and strongly dentate laterally; 



front with two tubercles, one above the other ■ • • • Diceratosmia. 

 Segment 6 more or less notched medially, not strongly sinuate or dentate- • .4. 



4. Ventral segment 1 emarginate; notch on 6 above broad, shallow; joint 4 of 



antenna about equals 2 + 3 Xanthosmia. 



Ventral segment 1 entire 5. 



5. Antenna monilifonn ; hind metatarsus arcuate, clavate ; hind spur large. 



Monilosmia- 

 Antenna filiform ; hind metatarsus and hind spur ordinary Osmia. 



TRYPETINI. 



Females. 



Section 3 of vein III longer than III, ... -2. 



Section 3 of vein III not longer than IIIi ; mandibles tridentate ; scopa whitish. .1. 



1. Segment 1 subtruucate, with a punctate concavity bounded by a salient rim ; 

 mandibles short, broad ; joint 1 of labial palpi less than one-half as 

 long as 2, 3-4 lateral ; coarsely punctured Trypetes. 



