76 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 52. 



is small, rounded, not longer than thick, and the second segment 

 exceeds in length any of those following it. In the male, except in 

 the case of a few species, the flagellum bears secondary sexual modifi- 

 cations that serve as specific characters. They consist of pits, 

 spines, dilations, curvings, etc., on various flagellar segments. 



The thorax is strong, compact, and flattened above. The pro thorax 

 is never strongly developed; the collar is much below the level of 

 the scutum and the tubercles do not reach the tegulae. The sternum 

 and episternum of the mesothorax are fused, leaving no suture. 

 The junction of the metapleura and the side of the median segment 

 forms a depression into which the femur of the middle leg is drawn 

 when at rest. The median segment is short and its dorsal surface is 

 lower than that of the thorax. The dorsal median area, or middle- 

 field, is definitely set off by oblique sutures and is broadly continued 

 down upon the almost vertical posterior surface of the segment. The 

 lateral angles are usually somewhat prominent but are always rounded, 

 never angular or wedge-like. 



In general appearance the abdomen is relatively compact and 

 robust, more rarely somewhat slender. The tergites are strongly 

 arched, the sternites flat. The ultimate tergite of the female is 

 somewhat conical in form, rarely with a pygidial area differentiated, 

 for the most part hirsute and provided with short lateral spines near 

 the base, usually punctate, but in a few cases more or less strongly 

 rugose. The second sternite of the male may or may not bear a 

 more or less well developed process, but the sixth, except in a very 

 few species, always does so. The form of these processes affords 

 specific characters. The seventh also varies in development and 

 the eighth, which is concealed by the seventh, ends in a single spine. 



The male genital armature consists of a short basal piece (cardo), 

 which bears the lateral stipites, the median cleft spatha and below 

 this the sagittae. The stipes, which alone is figured in the accompany- 

 ing plates, and which should never be left out of consideration in 

 the determining of species, is prominent and variable in form, accord- 

 ing to the pattern of which the species may be separated into groups. 

 Its variation in form among the groups is very marked. Its variation 

 within the different groups is sometimes very slight, so that, unless 

 it is supported by other characters, simply a slight variation in the 

 form of the stipes can not be regarded as safe ground on which to 

 separate species, for slight variations in the stipes occur among 

 individuals that are manifestly members of the same species. The 

 median cleft spatha terminates below in a pair of recurved hooks 

 that vary in form among the species and at a short distance proximal 

 to these hooks is a pair of short, sharply pointed, barb like teeth. 

 Below the spatha lie the sagittae, each of which is composed of two 

 parts, the one short, pointed, straight, and strongly hirsute; the 



