2 GEO. H. HORN, M. D. 



terial which he kindly placed at Qiy disposal for study in conjunction 

 with my own specimens. This aggregation of material has enabled 

 me to study the limits of variation, sexual and specific, and by this 

 means to fix with absolute certainty the species at present known. 



Several important facts have been learned. The first is, that the 

 characters heretofore used in the separation of species based on color, 

 sculpture, and the mode of dentation of the sides of the thorax, 

 have an extremely small value. The second is, that the form of the 

 antennae, together with the sexual peculiarities of the male, afl^ord 

 the only means of specific definition. 



In the four species known to me there will be observed two forms 

 of antenna. Three species, of which ferrvginea may be taken as 

 the type, have the joints of the antennae 4-11 of nearly equal length, 

 or, if anything, the outer joints are gradually a little longer, esjie- 

 cially the eleventh. In albida the outer four joints are notably 

 shorter than the four preceding joints in both sexes. 



At this point it is well to observe that the females of all the spe- 

 cies have a semicircular depression of the last ventral segment, fim- 

 briate with moderately long hairs. The last male segment is sinu- 

 ately truncate, without depression. Other sexual peculiarities exist 

 in the posterior tibiae of the males of several species, which will be 

 referred to in their proper place. 



The thorax is always more or less angulate at the middle of the 

 sides, and often with three small acute teeth. In a large series of 

 any species it will be noticed that in the males there is a tendency 

 to a simple angulation of the sides, while in the female it is more 

 common to observe the tridenticulate form. In albida both sexes 

 are similarly angulate, and it is rare to find one showing evidences 

 of the tridenticulation. In all the species the thorax is densely 

 coarsely punctured, a little less densely and with more shining sur- 

 face in carinata than in the others. 



The elytra are always more or less costate. At least traces of 

 four costse may be seen on each elytron. The innermost costa is 

 separated from the suture by three irregular rows of punctures, it is 

 often obliterated, and even in its greatest development {carinata) 

 does not extend more than three-fourths to apex. The second costa 

 is separated from the first by three irregular rows of punctures, and 

 is more constant in its distinctness, and is, when present, entire. 

 The third costa is always short, and is observed between the posterior 

 termination of the second and fourth costse. The fourth costa is 



