202 
Psyche 
[December 
Literature Cited. 
Cockerell, T. D. A. 
’96 The Bees of the Genus Perdita F. Smith. Proc. Acad. 
Nat. Sci. Philadelphia, vol. 48, pp. 25-107. 15 Figs. 
Cockerell, T. D. A. and Robbins, W. W. 
TO An Introduction to the Study of Rocky Mountain 
Bees. Univ. of Colo. Studies, vol. 7, pp. 179-195,51 
figs. 
Custer, C. P. 
’28 The Bee That Works in Stone; Perdita opuntice Cock- 
erell. Psyche, 1928, in press. 
Malyshev, S. 
’25 The Nesting Habits of Spiral Horned Bees of the 
Genus Systropha Latr. Rev. Russe d’Entom., vol. 19, 
pp. 21-26, 2 figs. 
Robertson, Charles 
T2 Origin of Oligotropy of Bees (Hym.). Entom. News, 
vol. 25, pp. 67-73. 
