Sept., i9i6.] AcKERMAN : Carpenter-Bees OF U. S. 203 



or glabellum of some authors. The mesonotum is sHghtly wider 

 anteriorly and its surface, except on the disk, is usually densely and 

 finely punctate with varying amounts of pilosity. The front margin 

 is slightly convex. The lateral margin is emarginate to a point be- 

 hind the tegula, then turns outward and downward slightly. Here a 

 sharp angle separates the dorsal surface of this plate from a nearly 

 vertical portion which extends backward to the anterior margin of 

 the side of the scutellum and largely concealed by the fore wing. 

 The posterior margin usually is quite straight. 



The scutellum, situated directly behind the scutum, is separated 

 from it by a distinct suture. Its surface is somewhat variable, being 

 either well rounded or flattened above and turning downward sharply 

 behind. Its front margin above is transverse but at the sides extends 

 forward, while the hind margin is curved backward more or less. 

 Along the lateral forward extensions is a small, somewhat fused 

 plate on each side, which occupies the anterior half and terminates 

 at the front wing process. The scutellum is densely punctured ex- 

 cept on the anterior median surface and its pilosity /:orresponds to 

 the number of punctures. 



The mesopleuron is made up of the epimeron and the episternum. 

 The former is composed of two plates, the anterior, smaller one being 

 situated a little above the posterior, and lying just above and behind 

 the pronotal lobe at the base of and partly concealed by the tegula. 

 Along the lower margin of the posterior plate is a well marked su- 

 ture which separates it from the episternum and which terminates 

 just above the middle of the anterior margin of the pleural plate of 

 the metanotum. The episternum is the very large lower plate of the 

 mesopleuron. It is convex, densely punctured and pilose. Below, it 

 is fused with the mesosternum with no suture between to show the 

 limits of each. The mesosternal portion is concave with a slight 

 longitudinal suture extending along the median line. 



The post-scutellum, as shown by Snodgrass in his excellent work 

 on the thorax of Hymenoptera (Proc. of U. S. Nat. Mus., Vol. 39, p. 

 53, 1910) is entirely concealed within the body between the meso- 

 thorax and the metathorax. However, since systematists generally 

 apply post-scutellum to the true metanotum, I shall use this practice 

 in the present paper so as to prevent confusion. 



Metathorax. — This segment is very small and compressed, lying 



