422 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 117 



from base to apex, feebly arcuate to almost straight, finely margined, 

 basal angles rectangular, apical angles broadly rounded, surface uni- 

 formly finely, shallowly, and densely punctured. Elytra with sides 

 nearly parallel to feebly arcuate, striae feebly impressed, finely and 

 shallowly punctured; intervals flat to subconvex, minutely, rather 

 sparsely, but usually distinctly, punctulate, even at low magnifications. 

 Prosternal process variable, never extremely convex between coxae 

 and not horizontal but tending toward the two extremes even among 

 individuals from the same population. Ventral surface of pronotum 

 concave, not thickened, finely and sparsely punctate to smooth; 

 metasternum finely and densely punctate medially, smooth or with 

 a few scattered coarse punctures caudo-laterally ; metepisternum with 

 a few scattered coarse punctm-es; abdominal sternites all finely and 

 densely punctured, punctures becoming coarser on lateral portions 

 of each segment. Male aedeagus with basal sclerite unusually large, 

 about 1.7 times the length of the parallel-sided apical sclerite 

 which has the apex acutely pointed, base truncate (pi. 5, figs. 38, 39). 

 Measurements: length 4.6-7.8 mm.; width 2.6-4.1 mm. 



Remarks. — This species may be separated from all other mem- 

 bers of the genus Platydema known to occm' north of the Rio Grande 

 by the antennal coloration described above. South of this boundary, 

 positive identification is made troublesome by the addition of at least 

 two other quite distinct and obviously closely related forms. The 

 situation is further complicated by the existence in the literature of a 

 number of names which cannot with any certainty be associated with 

 any of these species, without consulting the types. 



One of these occurs at least as far north as Tamazunchale in San Luis 

 Potosi, Mexico, where on at least two separate occasions it has been 

 collected in company with P. nigratum. These two species occupy 

 the same range southward at least to Panama. Champion (1886) 

 has referred to this second species as P. sobrinum Chevrolat, but 

 specimens submitted to M. Villiers did not compare at all with the 

 type in the Paris Museum. For the piu-poses of the present study 

 it will remain nameless. 



P. nigratum may be known from this second species by its more 

 parallel form, its more coarsely and densely punctured head, and its 

 much less convex pronotum, which is always distinctly and fre- 

 quently coarsely and densely punctured, and the finely but almost 

 always distinctly punctured elytral intervals. Each is clearly recog- 

 nizable and no intergradation of diagnostic characters has been 

 observed in the material at hand. 



A third species, closely resembling the two described above, pos- 

 sibly represents a distinct species apparently undescribed. It most 



