JFossorial Ihjmennptera of North America. 389 



The differences between the closely allied genera Pemphrcdon and 

 CemonvA are best brought out by a comparative description. In the 

 former the front narrows more rapidly, towards the mandibles the clypeal 

 region is more prominent, the sides of the head retreat more posteriorly. 

 The shorter triangular enclosure of the propodeum the shorter abdo- 

 men, thicker, and with a longer pedicel, distinguish the present genus. 



Cemonus inornatus, Ilarr. 



Pemphrcdon inornatus. Say, Long's 2d exp. App. p. 339, (1824). 

 Cemonus inornatus, Harr., Cat. Ins. Mass. p. 68, (1835.) 



Smith, Cat. Hyin. B. M. iv. p. 434, (1856). 



% . Entirely black. Head with a prominent vertex, polished, 

 shining, with scattered shallow broad punctures, from which arise 

 griseous hairs; anterior ocellus much smaller than the posterior 

 ones; in front of them the surface is puncto-striated ; towards the in- 

 sertion of the antennas, and on the clypeal region the hairs are longer, 

 dense, silvery, extending part way up the orbits. Mandibles sparingly 

 punctate externally, surface highly polished beneath, a few long setose 

 hairs ; antennas brown towards tips ; palpi pale testaceous ; surface of 

 the thorax polished, with sparse shallow punctures, as on the vertex of 

 the head ; mesoscutellum more densely punctured than the scutum ; 

 propodeum with the enclosure very distinct, short and broadly trian- 

 gular, with a broad mesial furrow gradually narrowed to the apex of the 

 enclosure, with small transverse rugulas; at base of the enclosure is a 

 row of longitudinal rugas, which increase in length towards the fur- 

 row ; this area is bordered on each side by a smooth polished convex 

 ovate-lanceolate oblique liuibus, which forms the outer side of the tri- 

 angular enclosure ; posteriorly the propodeum is coarsely and thickly 

 punctured on each side of the deeply channeled mesial furrow, becoming 

 less striated towards the insertion of the abdomen. Wings clear, or 

 partially clouded externally, iridescent. Legs black, tarsi sericeous. 

 Abdomen with a pedicel equalling in length the depth of the body of 

 the region ; smooth and polished on the sides; punctured and rugose 

 above; terminal rings a little paler on the posterior margin, especially 

 beneath ; hirsute and sericeous towards tip. 



Length of body, .17 — .20 inch. 



9 . Differs in the usual sexual characters, possessing a much more 

 cubical head, but with the same sculpturing, as also in the propodeum. 

 The tip of the abdomen has a short deeply sunken fossa or groove, the 

 body of the abdomen is longer, and the pedicel proportionally shorter 

 than in the other sex. 



Length of body, .20 — .30 inch. 



