184 BULLETIN m, UNITED STATES NATIONAL MUSEUM. 



hairs on the tips of apex and appendage, and also at the external angle 

 of the fossa on or beneath the apical angle of the dorsal plate. 



Internal lobe of the apex developed, the external rudimentary. 



Appendage variable, from conical to depresso-semi-ellipsoidal. 



Dorsal plate oblong and more or less strongly concave, the margins 

 being reflexed. 



Suhmarginal groove more or less visible from above. 



Superior pudendal membrane never reaching beyond the middle 

 of the dorsal plate and narrowly exposed. 



The following groups may be defined : 



All those species that have the first joint of the protarsi in both sexes thick- 

 ened at apex beneath and bearing a tnft of modified spinules upon the same; 



humeri obtuse Obscura Group. 



All those species that do not have the first joint of the protarsi thickened at 

 apex beneath and without a tuft of modified spinules; grooves entire. 



Humeri obsolete Grandicollis Group. 



Humeri obtuse Dentipes Group. 



The Dentipes Group is divided into the following sections: 

 Section A. — All those species which are genetically related by 

 having the inferior surface of the cauda, when present, formed by 

 the dilated apical extremity of the epipleura\ Such species are more 

 or less opaque and more or less asperately sculptured. 



Section B. — All those species which are genetically related by having 

 the inferior surface of the cauda, when present, simply nuirgined by 

 the undilated apical extremity of the epipleura? ; the inferior surface 

 of the cauda being formed by the general internal surface of tlu^ 

 elytra. Such species are glabrous and more or less shining and never 

 distinctly asperately sculi)tured. 



OBSCURA Group. 



This group may be characterized by having the first joint of the 

 protarsi distinctly thickened at apex beneath, and bearing a tuft of 

 modified spinules upon the same. In the males the protibial spurs 

 are somewhat equal in size, although the posterior may be slightly 

 longer than the anterior ; in the female the posterior spur is more or 

 less thickened and distinctly longer, and in both sexes the spurs are 

 decidedly divergent. 



The constituents of this group are among the largest of our species. 



The articular cavities of the tibiir are open and continuous with the 

 tarsal grooves of the same. The middle lobe of the mentum and the 

 exposed surfaces of the basal divisions of the maxillary palpi are more 

 strongly and conspicuously setose than in any other species known 

 to me. 



The head appears to b(^ comparatively long, and the abtlomen is 

 more or less distinctly ()bli(|iie in the male. 



