NORTH AMERICAN COLEOPTERA. 19 



4. — Sides of thorax behind the front angles straigiit, the transparent border be- 

 ginning at the front angles rectus. 



Sides of thorax arcuate in front, the transparent border beginning at the 

 sinuation. 

 Disc of thorax coarsely punctured, the two discal fovese on each side 



united by a deep gioove between them puiiclicollis. 



Disc of thorax sparsely punctate, the discal fovese separated. .discref us. 



Disc of thorax inipunctate, the discal fovea separated uititlus. 



5. — Prothorax coarsely punctate, the lateral fovese deep and broad. 



cribric'ollis. 

 6. — Median line of thorax distinct, extending two thirds the length of thorax..". 



Median line of thorax extremely short or wanting 8. 



7. — Discal fovese of thorax of the usual form, but at times shallow. 



Discal fovese deep, the lateral shallow, transparent margin beginning near 



the front angles iuterruptus. 



Discal fovese feeble, the lateral deeper; transparent margin beginning 



about one third from apical angles attritus. 



Discal fovese of thorax forming fine sinuate lines, disc rather flat ; trans- 

 parent border very narrow, beginning at middle lineatus. 



8. — Discal impressions of thorax forming a continuous line ; lateral fovese broad 



and moderately deep sculptus. 



Discal impressions very vague, the posterior pair only distinct, these forming 

 broad shallow depressions which are indefinitely confluent posteriorly ; 

 lateral fovese formed of indistinct sinuous depressions. 



Holmbergi. 



The various subgeneric divisions into which our species seem most 

 nearly to fall have been indicated in the preceding table, but with 

 the exception of Cyrtochthebius, Triimochthebins, and probably Ho- 

 malochthebius, the references are to be taken rather as parallels than 

 positive references. As already intimated the divisions are mere 

 tabular conveniences, and the advisability of attaching to them poly- 

 syllabic names seems doubtful. 



O. benefossus Lee. — Piceous, surface slightly bronzed, legs pale. Thorax 

 rapidly, arcuately narrowing from slightly in front of middle, the notch thus 

 formed having a very narrow transparent border; apical margin sinuate at the 

 front angles; disc very convex at middle, the sides beyond the lateral fovese 

 rather flat; surface sparsely punctate; median sulcus rather broad and deep, 

 discal fovete deep, separated, lateral impressions deep, broader at each end, 

 usually entire, sometimes separated into two elongate triangular fovea. Elytral 

 margin distinctly explanate from base to apex, disc convex, strise not impressed, 

 composed of moderately large punctures, separated by their own diameters. 

 Length .06 inch. ; 1.5 mm. PI. ii, fig. 1. 



In this species the labrura is feebly triangularly notched at middle. 

 The specimens from which Dr. LeConte described the species were 

 part of my collection, and were the (mly ones with the deeply sinuate 

 sides of the thorax in which the transparent border seemed absent, 



