HENRY J, FRANKLIN. 215 



two-thirds of the way across toward the hind end of the 

 biting edge. The mandibles of the male are bidentate in 

 both genera, the front tooth being the smaller, and in most 

 species they are heavily beardered on their outer faces, espe- 

 cially toward their bases (figs. 33 and 38). 



Thorax. (Figs. 1 and 2). 



The apparent thorax, as in most other Hymenoptera, in- 

 cludes, in addition to the thorax of other insect orders, the 

 first abdominal segment. This segment and the plates of 

 the meta- and mesothorax and the pronotum are firmly joined 

 together and form a box, the parts of which are practically 

 immovable in relation to one another. This box is as wide 

 (from side to side) as it is long (from front to rear) and 

 wider than it is deep (dorso-ventrally). Viewed posteriorly 

 or anteriorly (with the head and abdomen removed), it ap- 

 pears nearly round. Viewed laterally, it appears nearly tri- 

 angular. 



The most striking features of the thorax are the following : 

 (1) The great development of the mesonotum and meso- 

 pleura is accompanied by a great reduction of all the sterna 

 and of the metathorax. (2) The lateral and ventral parts 

 of the prothorax are suspended loosely in a large membran- 

 ous area which is continuous anteriorly as the neck. They 

 thus form a sort of suspensorium for the front legs, which is 

 easily detached from the rest of the thorax. (3) The pro- 

 notum is solidly attached to the anterior edge of the meso- 

 thorax, and its lateral parts extend downward till they meet 

 on the venter behind the prosternum. (4) The post-notum 

 (post-scutellum) of the mesothorax is entirely invaginated 

 into the cavity of the thorax, thus being invisible externally, 

 and is reduced to the form of two lateral arms of the large 

 internal postphragma. 



Having considered the general appearance and make-up 

 of the thorax, we may now proceed to a more detailed de- 

 scription of it. 



Prothorax. — The head is attached to the thorax by means 

 of a very flexible membrane. The place of attachment on 



TRANS. AM. ENT. SOC. , XXXVIII. 



