90 GEO. H. HORN, M. D. 



"sponiry" space may occur, sometimes as a very narrow border alonoj 

 the iniddle of the hind margin and often as a hoof-shaped space 

 usually of small extent. 



The other abdominal segments present nothing of moment except 

 mfimhriatus and picipes^ in which the first two segments at middle 

 are elevated in a carina. The last dorsal segment has a tolerably 

 uniform structure in all the species, the tip being four dentate, the 

 middle teeth more prominent, the lateral shorter and usually rect- 

 angular. In several species the middle teeth unite forming an obtuse 

 process. The sixth dorsal presents nothing peculiar, the margin is 

 either truncate or very slightly sinuate. 



J^cmalcs. — Anterior tarsi not dilated. 



The structure of the terminal abdominal segments is much more 

 complicated and difficult of description than in the males. To render 

 the subject plainer it is well to start with the simpler form which 

 occurs in luridus and nigrkornis. In these the last ventral is said to 

 be entire; it is wider than long, the sides regularly arcuate forming 

 an oval tip. The tip is fimbriate with short, equal spinules, for a 

 distance about equal to a fourth of the entire free edge of the seg- 

 ment, this fimbriate space is limited on each side by a minute tooth 

 bearing a long, slender seta, and half-way between this and the ante- 

 rior angle of the segment is another small tooth bearing a seta. 



The next modification of this structure arises from the middle of 

 the tip being very slightly notched, separating the spinules into two 

 groups, while the lateral setae arise from two well marked teeth on 

 each side. This is the structure in circumcinctus. Parallel with this 

 modification another occurs in which the lateral teeth become developed 

 into processes, the middle lobe being thus rendered apparently longer 

 although still entire at tip and fimbriate, niinms, debilia. 



In angustatns the middle lobe becomes more deeply notched and 

 prominent, but the two processes thus formed are still broad and 

 with numerous spinules, the lateral teeth become more acute and 

 longer. 



From this form the development of the structure found in most of 

 the species can be easily seen. The middle processes become gradually 

 longer and more slender while the spinules degenerate into short hairs, 

 the lateral teeth gradually elongate and become spiniform processes 

 and their setse shorter and more slender. The most advanced species 

 in the slenderness of these processes is probably fimhriatus. From 



