32 Journal New York Entomological Society. [VoI. xvii 



1. 0. pectoralis Lee, Trans. Am. Ent. Soc, 1868, p. 51. 



The mental wedge is in this species as wide at summit as at base, 

 the summit not or but feebly emarginate, the front face longitudinally 

 a little concave, the rear face nearly flat. Using the phraseology of 

 Dr. Horn the clypeal margin is narrowly double ; that is to say, it is 

 slightly thickened or elevated with a well defined upper margin. The 

 head is without elevations. Length 6,5-7.5 mm. 



The species is rare in collections and I have seen only males. It 

 occurs in New Mexico and Arizona. 



2. 0. gnatho Fall., Trans. Am. Ent. Soc, 1907, p. 247. 



The mental wedge is much thinner at base (from front to back) 

 than in pectora/is, the summit emarginate and much narrower than 

 the base, the front face concave from top to bottom instead of from 

 side to side. There is a small tubercle at the middle of the clypeal 

 margin and behind this there is a slight concavity. The extraordi- 

 nary width of the head in conjunction with the strongly produced 

 mandibles constitute the most striking features of this species ; the 

 prothorax is also relatively wider as compared with the elytra than 

 usual. The following measurements (in hundredths of an inch) ex- 

 press these relations exactly, like measurements of my single example 

 oi pectoralis being given for comparison. 



Gnatho (type). Gnatlio. 



New Mexico. Yuma, Ariz. Pectoralis. 



Width of head 10. 1 7.8 6.8 



" prothorax 13. 9 10. 2 II. 3 



elytra 13.7 10.4 13.9 



" head relative to that of elytra.. .73 .73 .49 



The type from Mesilla, New Mexico, and several nearly similar 

 examples from Yuma, Arizona, are all that are known to me. The 

 length varies from 5.5 to 7.5 mm. 



3. 0. simplex Lee, Proc. Acad., 1854, p. 222. 



No male of this species is at hand and the tabular characters are 

 taken from Horn's Synopsis. The propygidial carinae are said by 

 Horn to be exactly parallel, but I find them to be a little divergent in 

 front, though very nearly parallel posteriorly. The upper tooth of 

 the front tibia is small and much nearer the base than to the median 

 tooth. The elytral intervals are wide, the striae very feebly impressed 

 and the strial punctures less conspicuously larger than those of the in- 



