300 pnocEEDINOS OF THE NATIONAL MUSEUM. 



head, iind which may be termed the neck, and the larger, posterior 

 portion articiduting with the mesothorax, which may be termed the 

 collar. The nock joins the head at the center of a circular concavity 

 of the latter, which permits a free movement of the head on the body. 



The dorsal surface of the neck is rather flat; at its posterior end 

 it suddenly broadens and unites with the anterior face of the collar, 

 the two faces being nearly or quite at right angles to each other in 

 some cases. On each side of the neck is a pronounced double suture 

 extending- ])ackward, the sutures in the posterior half separating some- 

 what, leaving a narrow plate between them which may be pleural in 

 its nature. Beneath, the neck is shorter, soon broadening and showing 

 a median longitudinal groove. After thus widening it narrows, fitting 

 like a wedge into the base of the collar, which enlarges, forming a pair 

 of lobes to each of which a coxa is articulated. 



The anterior face of the collar is quite high, rising nearly or occa- 

 sionally quite to the height of the mesonotum. Above, it forms a 

 rounded crest behind which the posterior face lies, often nearly paral- 

 lel with the anterior one, its lower edge articulating with the anterior 

 edge of the mesonotum. Sometimes the collar is closel}^ appressed to 

 the mesothorax; sometimes there is considerable space between them 

 above. At the sides the surface of the collar is nearly vertical, rather 

 triangular in outline and somewhat depressed near its middle, the ver- 

 tex of the triangle being the edge of the crest already referred to. The 

 width of the collar from front to rear varies in different subgenera, it 

 being most compressed in Proterosphex^ while in some of the other 

 subgenera it is quite broad and its anterior surface is rounded verti- 

 cally, thus making less than a right angle with the dorsal surface of 

 the neck. 



The lower back corner of the triangle forming the side of the collar 

 is prolonged downward and Imckward and ends about opposite the 

 middle of the posterior side of the fore coxa. From near the middle 

 of the hinder margin of the side of the collar a lobe projects backward, 

 coming in contact with the lateral margin of the mesonotum above, 

 and overlying a depression of the mesopleuron in which a stigma is 

 located and which it conceals. This lobe, called the "schulterbeule" 

 by the Germans, 1 have termed the prothoracic lobe. Its outline 

 varies somewhat in different subgenera. (Plate VI, figs. 1 and 2.) 



Mesothorax. — The mesonotum is a broad plate lying between the 

 fore wings and in front of them, extending to the hinder part of the 

 collar anteriorly' and to the prothoracic lobe at the sides It is some- 

 what convex, and its sides and posterior edge are bent slightly upward 

 or reflexed, forming a sort of flange varying in amount. Starting at 

 the middle of the anterior margin and extending back one-third to one- 

 half the length of the plate or even more, a groove is sometimes seen, 

 varying in width, depth, and in the degree in which its edges are 



