DIAPERINI NORTH OF MEXICO TRIPLEHORN 391 



species would be included in Platydema and the shiny ones in his own 

 genus, Histeropsis. Unfortunately, he did not follow his own system 

 himself and, as a result, it is exceedingly difficult to interpret the 

 results of his studies. 



Judging from the description, Pascoe's genus Ty phobia, based on 

 T. juliginea from Queensland, Australia, is a good Platydema. 

 It was distinguished from Diaperis by the fact that all the antennal 

 segments except the termmal one were obconical. 



For the North American species of Platydema, the surface lustre 

 character works reasonably well, except for a few species which are 

 either lustreless or only feebly shining but which actually belong to 

 the shiny group and vice versa. The fact that it is a useful character 

 cannot be denied. Virtually every worker has utilized it in some way 

 in his key to the species, a situation which could not be avoided even 

 in this study of the limited Nearctic components of the genus, but it 

 does not seem that it can be applied successfully at the generic level. 



The most satisfactory course is to regard Platydema as a large nat- 

 ural group, insufficiently understood at present to divide or to attempt, 

 by studymg male genitalia, surface lustre, and coloration, to define 

 species groups. This was done rather sucessfully by Gebien (1925) 

 for the Indo-Malayan species. He divided them into three groups 

 which he regarded as natural: 



1. Patterned, or at least pigmented species which are not me- 



tallic. 



2. Metallic or shining black species. 



3. Species with dull colored elytra. 



Much the same classification was followed earlier by Champion 

 (1886), who divided the Central American components of the genus 

 into five groups: 



1. Head of males horned or tuberculate. 



2. Dorsal surface unicolorous, shining. 



3. Dorsal surface unicolorous, lustreless. 



4. Dorsal surface maculated, shining. 



5. Dorsal surface maculated, lustreless. 



A similar system can be applied arbitrarily to the 19 North Amer- 

 ican species. Two broad groups may be recognized: 



1. More or less shining species having the apical sclerite of the 

 male aedeagus composed of two lateral lobes (P. ^'americanum" 

 group). 



2. More or less dull, lustreless species having the apical sclerite 

 composed of a single piece (P. "rujicorne" group). 



The P. "americanum" group is quite homogeneous, all members 

 being closely related and similar in general habitus. The other nine 

 species comprising the P. "rujicorne" group are rather heterogene- 



