56 THE CANADIAN ENTOMOLOGIST. 



Cockerell, Nebraska) visits, like citrinella, the flowers of a species 

 of Petalostemum; the other (wootonce Cockerell) occurs in New- 

 Mexico. Colorado and Nebraska, and is a visitor of Nuttailia 

 (Fam. Rosacea?). A more extended acquaintance with the bees of 

 this group inhabiting the prairies east and north of Nebraska may 

 prove that citrinella is simply a colour variety of per pallida. 



P. gerhardi, Viereck. Up to the present time this species has 

 not been found outside of the Lake Michigan dune region. A 

 visitor of the horsemint (Monarda punctata L.), it was described 

 from specimens collected at East Chicago, Indiana, by Mr. Win. J. 

 Gerhard of the Field Museum of Chicago. Last year several 

 specimens were taken by the writer in the dunes south of Kenosha, 

 Wis., on the flowers of the horsemint. I have come across this 

 plant in the Mississippi Valley as far north as Prescott, Pierce Co., 

 Wis., in some places growing in abundance, but in spite of a sharp 

 lookout for the bee P. gerhardi, no specimens were obtained. 



This species, a yellow Perdita, belongs to the perpallida —  

 wootonce — citrinella group discussed above; it has, in the female 

 sex (I do not know the male of citrinella), very much the appear- 

 ance of a small citrinella, differing from the latter in the size and 

 arrangement of the -black markings on the yellow background. 

 We are dealing with a species derived from the same source as 

 citrinella, but depending for pollen on the flowers of a plant belong- 

 ing to a different family (Labiatae) than that visited by citrinella, 

 and to a different region; it is a plant of the eastern United States, 

 the western range of which brings it in contact with elements of 

 the prairie region. 



SUMMARY 



Of the six species of Perdita known from Wisconsin, two are 

 visitors of the Compositse, two of the Leguminosae, one of the 

 ground cherries (species of Physalis), and one of the horsemint 

 {Monarda punctata). 



They are derived from the bee fauna of the Prairie Province, 

 and have followed in the wake of the floral prairie elements that 

 invaded the Wisconsin area. Albipennis, a western form, occupies 

 the centre of vegetation of the prairies, and ranges southward to 

 Texas. Grouped around this are three forms, one of which, lactei- 

 pennis, occurs together with albipennis in western Nebraska; the 



