THE CANADIAN ENTOMOLOGIST 51 



Immature individuals are entirely pale green. 



This species lives gregariously on the underside of the leaves 

 and tender terminal shoots of hazel (Corylus americana). De- 

 scribed from specimens collected at La Fayette, Ind., July 5, 1912. 

 The writer has also collected this aphidid at Chicago, 111., May 20 

 and July 10, 1908. 



(To be continued.) 



WISCONSIN BEES OF THE GENUS PERDITA. 

 GEOGRAPHICAL DISTRIBUTION AND RELATIONS TO 



FLOWERS. 



BY S. GRAENICHER, PUBLIC MUSEUM, MILWAUKEE. 



In 1896 Prof. T. D. A. Cockerell 1 published a paper on this 

 genus, containing a vast amount of information, and dealing with 

 the various aspects of taxonomy, variation, distribution, relations 

 to flowers, etc. 



The centre of distribution is located in the arid region of the 

 Southwestern United States, New Mexico having an especially 

 large percentage of species in its fauna. Prof. Cockerell states 

 "that in the main we have to do with an austral series of types, 

 which have spread northward and become largely differentiated 

 into species since the glacial epoch." A splitting up into a great 

 variety of forms is evident, and, as Prof. Cockerell puts it, "we have 

 indeed the process of evolution going on under our eyes, the puz- 

 zling forms being those which have only lately segregated 'them- 

 selves, and have not yet developed striking peculiarities." 



Another characteristic feature of this genus lies in the fact 

 that all of the species, so far as their habits are known, are oligo- 

 tropic, i.e., most of them depend for their pollen-supply on a 

 single species of flower, and those that collect pollen from a number 

 of plant species, favour closely related forms, belonging either to 

 the same genus, or at least to the same family. New Mexico and 

 Colorado offer extremely favourable opportunities for the study of 

 the close relations between the various forms of Perdita and the 



1. Proc. Acad. Nat. Soc. Phil., Vol. 48, pp. 25-107. Two years ago the 

 author published "A list of the bees of the genus Perdita Smith" in Psyche, 

 Vol. 18, pp. 134-143 (1911). 

 February. 1914 



