PROC. ENT. SOC. WASH., VOL. 24, NO. 1, JAN., 1922 13 



Throughout the genus the fronto-buccal region inclines for- 

 ward and downward (figs. 3 & 4). The frons is strongly 

 transverse, bounded laterally by the eyes and anteriorly by 

 the free margin of the frons (Fm, fig. 1). The frons is flat to 

 feebly convex in fissilis Say and in most other species; in 

 decumanus Er., it is strongly concave. The free margin of 

 the frons is distinct throughout the genus; rounded broadly 

 or acutely or subtruncate, according to the species; in a few 

 species deflexed over the fronto-clypeal region. 



Thefronto-c/ypea! region (FCL, fig. 5, M. fissilis Say) is the 

 area bounded laterally by the eyes, above by the free margin 

 of the frons, and below by the base of the labrum and the 

 insertion of the mandibles; it bears the antennal bases and is 

 always transverse. A suggestion of a suture on either side 

 below the antennal foveae separates vaguely the clypeus from 

 the frons. 



The fovea of the antenna (Ant Fov, figs. 3, 4 & 5) is located 

 near the lateral margin of the fronto-clypeal region and a little 

 above the middle. Leading from it in a downward and out- 

 ward direction is a shallow, opaque antennal fossa which in 

 some species continues across the exteiior basal part of the 

 mandible. Situated between the antennal foveae is another 

 pair of foveae, here termed the par antennal foveae (Prt Fov, 

 figs. 3, 4 & 5) which are extremely variable in form. The 

 parantennal fovea may be only a shallow impression (fissilis 

 Say and communis Gyll.) or a wide ear-shaped chamber with 

 deep recesses entering sideways into the cranium behind the 

 anterior face of the parantennal region (^Sagittarius Leconte and 

 Melanotus sp., fig. 3). For the taxonomically important area 

 between the parantennal foveae Dr. Boving suggests the term 

 parantennal region (Prt A, figs. 3, 4 & 5). Besides the foveal 

 differences, the shape of the parantennal region (transverse, 

 quadrate or vertical), and its plane with reference to the rest 

 of the fronto-clypeal region, promise to be of great value in 

 the taxonomy of the genus. 



In all the species examined the eye is nearly hemispherical 

 and somewhat emarginate at the lateral extremities of the free 

 margin of the frons. 



The labrum (fig. 6") is transverse, convex and coarsely punc- 

 tate; its superior margin straight, the sides and lower margin 

 broadly rounded. This structure varies little in shape through- 

 out the genus. On its inner face is the membranous epipharynx 

 which is partially visible below the lower margin of the labrum 

 (ep, fig. 6). 



Mandible. (Mnd, figs. 5, " & 8.) External part robust, 

 strongly curved, cleft near the apex, and in some species rugosely 

 punctate; the left overlying the tip of the right; the right man- 

 dible a little more strongly curved than the left. In some species 



