178 BULLETIN 63, UNITED STATES NATIONAL MUSEUM. 



Brimer; Dodge County, Coll. F. E. Blaisdell) ; Southern Dakota 

 (Alexandria; Volga, Coll. E. C. Van Dyke) ; Kansas (Gove County, 

 2,500 feet, F. H. Snow, Warren Knaus, Hubbard and Scliwarz; 

 Plains, Dr. George Horn) ; Colorado (Dr. George Horn; Trinidad; 

 Colorado Springs, F. H. Snow; AVest Las Animas, H. F. Wickham). 



Number of specimens studied, 38. 



Type not in existence. 



Type-locality as given by Say is Missouri and Arkansas. 



Sdtierit type-chafacters. — Opaque, clothed with whitish hairs; 

 thorax with acute anterior and obtusely rounded posterior angles; 

 sides hardly arcuate. Elytra with base emarginate to receive the 

 prothoracic base ; humeral angles acute; lateral edge- acute. Lateral 

 curve of the body continuous (Say). 



Diagnostic characterg. — Distinct from its congeners in having the 

 dorsal surface of the elytra quite Hat. with the lateral margins quite 

 acute; the surface is opaque and rather sparsely covered with short, 

 recumbent, setiform hairs. 



It resembles fusifornus in having the anterior femora unarmed 

 and in having the elytral base deeply emarginate with the humeral 

 angles embracing the obtusely rounded basal angles of the ])rothornx. 



Structurally these two species are closely related and undoubtedly 

 originated from the same basic stock. In opaca the elytral base more 

 strongly clasps the prothoracic base than in fusiformls^ and in the 

 latter more than in striolata, where this character is at its minimum, 

 and entirely al)sent in yoryi, siibnitens, and insularis. 



It is to be observed that the relations of the prothoracic and elytral 

 b^ses give to the lateral margins of the insect a continuity of outline 

 which is most marked in opaca and the least developed in insvlaris, 

 these two species constituting the extremes of the subgeneric series. 



Mr. Say, in his description of the species, says that the " lateral 

 edge " of the elytra is not reflected, but in all the specimens before 

 me it is slightly and distinctly reflected in basal half of the elytra 

 and gradually becomes evanescent as it approaches the apex. 



Variations. — In a series of seven specimens collected at Fort Sup- 

 ply, Oklahoma, and Mobeetee, Texas, there is distinct evidence of 

 three elytral costa? — in other words, the sutural and every fourth 

 interval is feebly but noticeably convex, with feebly but clearly 

 defined stria? of fine and closely placed punctures. Normally the 

 " elytra are destitute of stria^." 



General ohser rations. — The mentum is variable, usually triangular 

 and rounded at apex, or less frequently subparabolic in outline; sur- 

 face feebly convex and more or less foveate laterally. 



Prosternum evenly arcuate antero-posteriorly in the median line, 

 sometimes horizontal between and behind the coxse; produced pos- 

 teriorly into a more or less strong mucro, which is usually compressed 



