AMERICAN COLEOPTERA. 6 



degree of prominence of the posterior spiracle appears to me 

 to be of no use whatever. On the other hand, the position 

 and form of the ungual tooth, and the form of the clypeus are 

 of prime importance. To these I would add a third of nearly 

 equal value, viz. : the structure of the mentum. Of these, 

 the first named is least subject to individual variation, but 

 taken throughout the series there is a complete gradation from 

 one extreme to the other, and its use is therefore impracticable 

 as a group character. The form of the clypeus while very 

 useful, varies not infrequently within specific limits to a con- 

 fusing degree; here, too, there is every intermediate form 

 between the extremes. The form of the mentum is especially 

 serviceable in certain parts of the series, but it also possesses 

 in greater or less degree the failings of the other two. In the 

 absence of group characters it has been found convenient to 

 place at the beginning of the series those species which have 

 the upper surface wholly or in part hairy or pubescent. They 

 do not constitute a natural group, but the character being a 

 perfectly definite one, tabulation is thus facilitated. Some 

 preliminary discussion of certain structural details and of the 

 significance of certain terms used may aid the student in his 

 use of the table and in reading the descriptions which follow. 

 With the single exception of abnormis (with 9-jointed an- 

 tennae) all the known species of this genus have the antennas 

 10-jointed. These organs are monotonously similar in struc- 

 ture throughout the genus, and have yielded no specific char- 

 acters. There are, it is true, some — usually slight — differ- 

 ences discernible in the relative lengths of club and stem, but 

 these have not been thought of sufficient moment to describe. 

 The labrum is usually broadly arcuately emarginate, and is 

 to be so understood when not otherwise described. In mcerens 

 and peninsularis the emargination is much deeper, and in 

 popino, mimoscz and cribrulosa of the hairy species, and knausii 

 and fissilabris of the glabrous ones this organ is so deeply 

 divided as to merit the term bilobed. The two last named 

 species are further remarkable in that the mentum is also 

 excavate in front. In the majority of species the elytra 

 possess a more or less minute granulato-reticulate sculpture, 



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



