Sept., I9i6.] ACKERMAN : CaRPENTER-BeES OF U. S. 205 



overlaps the small ventral sclerite on each side. The anterior face 

 presents a large, median, concave area, the excavation being widest 

 at its lower end. The punctation of the dorsal surface of this seg- 

 ment is finer and denser than on any of those that follow, while the 

 pilosity is rather thick and often is present as a tuft on either side. 



On the dorsal surface of segments two to five inclusive the puncta- 

 tion is quite well marked and dense, especially along the sides. The 

 dorsal surface, however, is naked and shining in many species though 

 in others there may be a little pubescence present, which is most 

 noticeable along the hind margin of the segments. Each segment 

 consists of a dorsal and a ventral sclerite, the former overlapping 

 the latter on each side. The last segment of the female is more 

 pointed than that of the male and the sides of the dorsal sclerite over- 

 lap the ventral sclerite as in the preceding segments. On the dorsal 

 surface of the female are two rows of short spines which converge 

 toward the apex. These are called the epipygium in this paper. 



In the male the last dorsal sclerite (the seventh) overlaps the 

 sixth sternal plate, since in this sex there are only six sternal sclerites 

 while there are seven dorsal ones. A pair of styli or cercus-like 

 pieces, known as penicilli, occur at the tip of the last visible dorsal 

 plate among males of two species, ovpifcx and tabaiiifoniiis. The 

 pilosity of the last segment is caused by long and dense hairs, a fact 

 frequently made use of in classification. A slight median longitudinal 

 carina often occurs in the dorsal and ventral plates of the entire 

 abdomen. 



Sting. — This organ is situated in a cavity at the end of the abdo- 

 men and is a tapering shaft which is directed backward. It consists 

 of three plates, a dorsal one and two ventral ones. The dorsal plate 

 is called the sheath and forms the upper and side areas of the sting; 

 its greatly swollen basal portion is termed the bulb. Ventrally at the 

 base of the bulb are two lateral arms which curve inward and upward 

 to form the ventral plates of the shaft. These arms are called the 

 lancets or darts which slide along tracklike grooves found on the 

 ventral edges of the dorsal plate. 



Between the lancets two poison glands empty into the bulb. 

 Within the bulb and running the length of the shaft is the sting canal 

 which receives the poisonous secretions. The distal ends of the lan- 

 cets are barbed on either side. Surrounding the base of the shaft 



