484 Mr. T. D. A. Cockerell — Descriptions and 



white, a fringe of long white hairs at apex ; head broad, 

 quadrate, finely and very densely punctured; mandibles black ; 

 mesothorax and scutellum densely punctured ; area of meta- 

 thorax dull and granular. Wings hyaline. Tarsi with red 

 hair on inner side ; anterior tarsi with joints 2 to 4 having the 

 anterior apex produced ; middle tarsi with basitarsi obcordate, 

 very short, and greatly swollen, very hairy, the hair mostly 

 fuscous ; hind basitarsi also broadened, but not so short, the 

 inner margin with a prominent angle beyond the middle, the 

 anterior face shining, not hidden by hair ; spurs of hind legs 

 dark, curved at end, not peculiar ; small joints of middle and 

 hind tarsi thickened, but not otherwise remarkable. Abdo- 

 men shining, sixth segment with a scarcely noticeable trace 

 of an emargination, seventh strongly bidentate ; second 

 abdominal segment thickened on the apical middle; third 

 deeply emarginate, the sides of the notch with a short fringe 

 of orange hair. 



$ . — Length about 10 mm. 



Robust, tegumental colours like those of male, but clypeus 

 and adjacent sides of face blue-black, supraclypeal area green, 

 and face on each side of antennae steel-blue; mandibles tri- 

 dentate ; clypeus subemarginate ; hair of face long and 

 entirely black, of cheeks up to sides of vertex black, but of 

 head and thorax above pale orange-yellow, not mixed with 

 black ; middle of mesothorax with well-separated punctures ; 

 pleura and metathorax with black hair. Legs black, with 

 black hair, except on anterior tarsi, where it is pale ; first 

 abdominal segment with yellowish-white hair, the others 

 with black, the hair quite long and coarse; ventral scopa 

 black. 



Flab. Nebraska Hill, Colorado, at flowers of Trifolium, 

 above timber-line, July 1915 {L. A. Kenoyer). 



Known from all other North-American species by the 

 structure of the male tarsi. The female may be compared 

 with 0. hendersoni, Ckll., but the abdomen is quite differently 

 coloured and the sixth segment has not the pale reddish hair- 

 fringe seen in hendersoni. The abdomen of hendersoni is 

 smoother and less hairy. In Friese's tables of Palsearctic 

 Osmia both sexes run near 0. angustula, but are quite 

 distinct from that species. Also on Nebraska Hill, above 

 timber-line, but not on a flower, Mr. Kenoyer took a male 

 Osmia abnormis, Cresson. On Nebraska Hill, at Salix, 

 100 feet below timber-line, Mr. Kenoyer took Ilalictus 

 sisyntbi ii, Ckll. 



