AMERICAN COLEOPTERA. 5 



position of the impression the well-known species tristis and 

 libcrta may be cited; in the former it is very nearly at the 

 middle of the elytra, while in the latter it is just behind the 

 humeral umbone. The apical marginal groove of the propygi- 

 dium is another character so generally present, that reference 

 is rarely made to it, except in the few species in which it is 

 feeble or absent. In many species the second ventral seg- 

 ment and sometimes the third and fourth exhibit at the middle 

 a more or less obvious series of short parallel ridges or grooves, 

 which in a smaller number of species (e. g., knausii, brevicollis, 

 levicoxa, haydenii) are replaced or accompanied by an obtuse, 

 more or less plicate tubercle on each side of the middle. This 

 sculpture varies greatly in development in individuals of the 

 same species and is possibly in some degree sexual; and because 

 of this variability little or no mention has been made of it in 

 the descriptions. The variations in the structure of the men- 

 turn will be best appreciated by an examination of a few of 

 the typical forms, while the differences in the form of the 

 clypeus and claws are fairly well shown by the outline figures 

 of the plate. 



Secondary sexual characters are not entirely wanting, but 

 with a few exceptions they are of such a nature that it is 

 rarely possible to determine the sex of a single specimen, and 

 even in a considerable series containing both sexes, they can 

 rarely be separated with certainty. If from a series of speci- 

 mens of almost any species, those having the most slender 

 and the most robust hind femora be selected, the former are 

 almost sure to be males and the latter females; but the dif- 

 ferences are often very slight, and even when more pronounced 

 there are usually intermediates which to all appearances seem 

 as likely to belong to one series as the other. In addition to 

 this general distinction the following special sexual differences 

 have been observed, the characters in all cases pertaining to 

 the males. 



Terminal joint of maxillary palpi more broadly dilated — ■ 

 bowditchi, brevidens, tarsalis. 



Antennal club a little more elongate — bowditchi. This has 

 not been carefully investigated and there are probably others. 



Eyes larger — schaefferi, confusa. There are probably others. 



TRANS. AM. ENT. SOC, XXXV. JANUARY, 1909. 



