362 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 117 



two short carinate ridges on the frons near the epistomal margin. 

 The head of the female is completely unmodified. 



Except for the above-mentioned modifications, there is very little 

 that can be used in separating the two sexes. In North America, 

 this applies to most species of Platydema, three of the four species of 

 Diaperis, one of the two species of Pentaphyllus, and the genera 

 Palembus, Scaphidema, Lioclema, and Apsida, each represented in our 

 fauna by a single species. If a series is available, it is usually pos- 

 sible to separate most of the males from most of the females by 

 size and shape; the females generally are larger and broader. 



Geographic distribution. — Some genera of Diaperini are extraor- 

 dinarily widely distributed. The ubiquitous genus Platydema includes 

 species from every continent and many islands have species which are 

 peculiar to them (e.g., P. antennatum Laporte and BruUe, on Cuba). 

 Neomida is also cosmopolitan, but contains fewer species. If we 

 exclude the Ulomini with its many species widely dispersed through 

 commerce, the Diaperini are probably the most widespread of all 

 the Tenebrionidae, although a few genera are somewhat restricted. 

 Cosmonota is confined exclusively to Central and South America, 

 Ceropria to the Old World tropics, and Scaphidema to the Holarctic 

 region. 



Most of the individual species occupy moderately restricted ranges. 

 Only one, Alphitophagus bifasciatus (Say), can be considered cosmo- 

 politan. As might be expected, the tropics of both hemispheres 

 abound in species of Diaperini. The relative paucity of Nearctic 

 species stands in distmct contrast to the bewildering array of Neo- 

 tropical species, especially in the large genus Platydema. Liodema 

 and Apsida, both moderate-sized genera, each have but one species 

 represented north of the Rio Grande, the remaining species being 

 found only in Central and South America. 



The tribe knows no boundaries in North America. Individual 

 species, of com^se, may be categorized as southern or northern, eastern 

 or western, and very often exhibit interesting distributional patterns. 

 Some (e.g., Platydema excavatum, P. americanum, P. rujipes, and 

 Neomida bicornis) have exceedingly wide ranges, whereas others (e.g., 

 Platydema inguilinum, Diaperis rujipes, and D. calijornica) are ex- 

 tremely localized. 



Origin and phylogeny. — It would be impossible at this time to 

 advance a theory as to the origin of the group in its entirety. If 

 we regard as primitive the condition in v/hich the parameres of the 

 male aedeagus are unfused, then the americanum group of the genus 

 Platydema must be considered the most primitive element. This 

 group certainly has its metropolis in the Nearctic region; 9 of the 19 



