314 r.ro. h. horn, m. d. 



to be of sufficient moment or permanence to afford a basis for the sub- 

 division of the genus into genera of equal value among themselves. 

 These variations, however, afford good bases for the formation of 

 groups, and enable the species to be determined with great ease con- 

 sidering their small size and similarity of vestiture. 



The following sketch of the groups into which I propose to dis- 

 tribute our species may appear almost too mathematical to be correct 

 in nature ; they will be found, however, to be very persistent in each 

 species, and I have scarcely found in all the specimens examined any 

 variation in the number and position of the denticles of the hind 

 femur : 

 Thorax with tooth at middle of side. 



Hind femur with tooth on outer side only Gr. I. 



Thorax not toothed on the sides. 



Disc ot thorax elevated, with a median groove. 



(Hind femur with a strong tooth and three denticles) Gr. II. 



Disc of thorax simply convex, not elevated. 



Hind femur with a tooth on both inner and outer margins Gr. III. 



Hind femur mutic (antennse pectinate or flabellate % ) Gr. IV. 



Hind femur with one tooth only on inner margin Gr. V. 



Hind femur with one tooth and one denticle Gr. VI. 



Hind femur with one tooth and two denticles Gr. VII. 



Hind femur with one tooth and three denticles Gr. VIII. 



Hind femur with a few small denticles only Gr. IX. 



The tooth of the hind femur is situated at the distal end at about 

 one-fourth from the knee, on the lower edge and (except as noted 

 above) on the inner side. Between the tooth and the knee is an 

 euuargination of greater or less depth in which the denticles are situ- 

 ated. In Group IV. there isnotooth nor deuticleand no einargi nation 

 of the lower edge of the femur. The femur does not present in any 

 of our species that broad oval form which appears to be accompanied 

 by an extraordinary leapiug power. The nearest approach to it is 

 seen in B. mimus, Say, which resembles in its general aspect a diminu. 

 tive Pachymerus. 



Group I. 

 Thorax broader than sides moderately arcuate and with a tooth at 

 middle. Antennas scarcely larger than half the body, similar in the 

 two sexes, gradually thicker externally and subserrate. Posterior 

 femur with a strong tooth near the apex on the outer side. Middle 

 tibia; % more or less arcuate aud with a small tooth on the inner 

 margin near the tip. 



