Sept., I9i6.] ACKERMAN : CaRPENTER-BeES OF U. S. 199 



in July and August and hibernate in the middle states during the 

 winter months." 



Westwood, in his Classification of Insects, Vol. II, p. 278, says 

 that the bees form about a dozen cells, one above another, in one 

 tunnel. When the larvse in these cells are full grown they assume 

 the pupa state, head downward, so as to allow the lowermost and 

 oldest to make its way out of the bottom of the burrow as soon as it 

 becomes winged, and which consequently takes place earlier than in 

 those which occupy the upper cells. 



Davidson in Entomological News, 1893, p. 151, gives an article 

 on observations of Xylocopa orpifex in southern California. In 

 opposition to Westwood's statement he notes that the bees, after 

 hatching, all make their exit through the original opening; thus the 

 bees in the top cells come out first, while those in the lower cells, 

 which are the older, make their exit last. He suggests, as the reason 

 for this, that the bees in the upper cells are all males, while those 

 in the lower cells are all females. 



L. O. Howard, in Proc. of Ent. Soc. of Washington, Vol. II, p. 

 331, gives an article on hibernation of the carpenter-bees. He states 

 therein that the male as well as the female does hibernate. Pre- 

 viously it had been thought that the male does not winter over. 



External Anatomy. 



Head. — The head, which is hypognathous, is relatively large as 

 compared with the thorax. It is broad and usually rather thick, and 

 viewed from the front its form is subcircular in outline. Its size 

 varies somewhat but as a rule is wider and thicker in the female. 

 The face is usually slightly convex in profile and here the punctation 

 is most dense, while that on the vertex and cheeks is rather sparse. 

 The face generally bears but few short hairs, while the pilosity on 

 the cheeks, especially the lower half, is long and dense. 



The vertex is bounded posteriorly by the occiput and anteriorly 

 by an imaginary transverse line between the antennal pits. The 

 vertex in the males is narrowed toward the occiput and is likewise 

 narrowed on the front surface because of the marked approximation 

 of the eyes. In the lower portion of the vertex there is a pit which 

 surrounds the middle ocellus and is continuous with a median groove 

 on its lower margin. This median groove passes downward to the 



