214 GEO. H. HORN, M. D. 



Pygidium. — While the pygidium does not differ in the sexes very 

 materially in some species, in very many that of the female is much 

 more elongate, often more convex, the punctuation more defined and 

 the surflice more shining. 



Abdomen. — The differences are for the most part of a purely 

 sexual nature, and their description is given with each species. 



Legs. — As a rule the legs of the female are shorter and stouter than 

 in the male (fig. 8), This is especially noticeable in the front tibiae 

 and hind femora. The tarsi are all shorter in the female, moi'e per- 

 ceptibly in those of the hind leg. The greatest disparity in length 

 is observed in the species of the first and second groups, elsewhere 

 the difference is not so great, the usual ratio being — the first four 

 joints of the male hind tarsus are equal to the five of the female. 

 The only other tarsal modification is that of calceata (fig. 15). The 

 sexual differences in the claws have already been explained. 



The posterior tibise are either squarely or obliquely truncate at 

 apex, the edge continuous in all the species excepting those of Groups 

 VI and VII, in which in the males there is a sinuation of variable 

 extent at the base of the fixed spur from which a broad groove ex- 

 tends along the inner edge of the tibia (figs. 18-14). 



In the grouping of the species which follows I have adhered to 

 the characters used by Dr. LeConte, but have modified their use to 

 suit the greatly increased material. The subject has been a very 

 difficult one to treat, in the fusca group especially, from the tendency 

 to vary in those characters most serviceable in a synoptic table. 

 With a little experience there will be no great difficulty in referring 

 either sex to its appropriate group, but beyond that males alone can 

 be safely used. 



The following arrangement seems to give a fairly natural sequence 

 of the species : 



Hind tibiffi % with both spurs free 2. 



Hind tibisF, % with one spur fixed 5. 



2. — Species very robust, one or both sexes apterous ; hind tarsi %, very long, 



those of 9 scarcely longer than the tibiae 3. 



Species of usual oblong form ; both sexes winged 4. 



3. — Body clothed with scales ; thorax not narrowed behind. 



Group I, lanceolata. 

 Body glabrous; thorax widest at middle, narrowed at base as well as apex. 



Group II, farcta. 



4. — Inner spur of hind tibise % stout and contorted (fig. 12). .Group III, torta. 



Spurs of hind tibite % both slender 11. 



