182 HETEROMERA. 
name Histeropsis (this itself to contain four groups) various species; and Motschoulsky 
(loc. cit.), for a similar purpose, separates others under Neomida, a manuscript name in 
itself highly objectionable, it having been already applied to numerous widely different 
genera. I have not thought it necessary or advisable to adopt any of these so-called 
genera. . 
The smooth shining species have a different facies from the dull and opaque ones ; 
the eyes are comparatively smaller, the epistoma often not clearly defined, &c., but 
in general structure they agree. Two species (P. meaicanum and P. viriditinctum) 
resemble somewhat in form the European P. dytiscoides. 
Platydema is highly characteristic of the forest-regions of Tropical America, numerous 
species abounding in many localities. The different species are found in fungoid 
growths, on fallen timber, in which the earlier stages are passed, and in company with 
representatives of other groups of “Tenebrionide,” and of the Erotylide and Endo- 
mychidee, are everywhere to be met with. 
The following table will assist in the recognition of the numerous Central-American 
species :-— 
Head tuberculate or horned in the male. 
Intraocular space concave in the middle, a slender porrect horn on each 
side in the male, longitudinally raised on each side in the 
female; surface shining . . .. . . . . . excavatum. 
Intraocular space in the male concave in the middle, and longitudinally 
raised on each side, in the female slightly impressed; surface 
opaque. 
_ Elytra with angulated transverse paler bands . . . . . . . . wndatum, 
rodriguezi. 
Elytra dull black . 2. 2. 2. 1. 2 1 we we ee. hondurense. 
Head unarmed in the male. . 
Intraocular space distinctly impressed in the middle ; form more or less 
obovate, depressed. 
Upper surface shining, bronze black. . . soe ee we. viriditinctum. 
Upper surface slightly shining, brownish black see ee ew mexicanum. 
Intraocular space plane, or at most feebly impressed; form more or less 
ovate. 
Upper surface unicolorous, opaque. 
Dull black, rarely dark ferruginous. 
Form oblong-ovate or ovate . . . 1. 1 ss. 1 « agile, angulatum, 
subquadratum, sobrinum, ferrugineum, fuliginosum, melancholicum. 
Form rotundate . 
ee ee ew ew we . -rotundatum, 
rugiceps, oculatum. 
Dark reddish brown, pruinose ; form rotundate. . . . . . nicaraguense. 
Ferruginous ; form oblong-ovate. . . . . . . . . émmaculatum. 
