426 PROCEEDINGS OF THE NATIONAL MUSEUM vol. in 



and usually rather widely spaced; intervals flat to subconvex, im- 

 punctate. Prosternal process extremely narrow, horizontal, its apex 

 greatly prolonged behind and acutely pointed. Ventral suface of 

 pro thorax smooth and polished, impunctate; sterna and pleura of 

 meso- and metathorax practically smooth, with only a few minute, 

 widely scattered punctm'es; abdominal sternites finely, sparsely, and 

 rather uniformly punctured, usually with faint longitudinal wrinkles, 

 foiu-th sternite with prominent lateral impressions. Male genitalia 

 (pi. 5, figs. 43, 44) with apical sclerite drastically reduced, only 

 one-fifth as long as basal sclerite, entire aedeagus tapering gradually 

 to the acute apex. Measurements : length 3.2-4.4 mm. ; width 1.7-2.6 

 mm. 



Remarks. — This is one of the most easily characterized members 

 of the genus Platydema in the Nearctic region. The only other species 

 possessing frontal horns are P. excavatum, P. cyanescens, and P. teleops, 

 and all these are quite shiny in lustre with theu horns thin and sharply 

 pointed. The presence or absence of these horns cannot be considered re- 

 liable m establisliing relationships within this genus. A comparison 

 of the male genitalia of P. erythrocerum and the three other horned 

 species indicates that they stand rather far apart phylogentically. 



The affinities of this species clearly lie with the tropical P. undatum 

 Chevrolat, which occm-s at least as far north as Jalapa, Veracruz, 

 Mexico, and extends southward well into Brazil (Santarem). The 

 male genitalia illustrate a close relationship, but in P. undatum, the 

 horns of the male are reduced to small tubercles as in the female of 

 P. erythroceimm and the females lack even the tubercles. Both species 

 are dull in lustre and have the same antennal coloration. Whereas P. 

 erythrocerum is unicolorous, P. undatum is attractively marked with 

 variable bands of orange outlined in dark brown on a yellow 

 ground color. Two other species, P. rodriguezi Champion and P. 

 hondurense Champion, according to their descriptions, should also 

 prove to be members of this species group. 



Type. — Not seen. The description is quite adequate to establish 

 the identity of this species. According to Laporte and Brulle (1831), 

 "Get insecte habite L'Am^rique meridionale." This I have inter- 

 preted to mean southern North America and not South America. The 

 type of Neomida jiavicornis (UMMZ) corresponds to specmiens from 

 Mississippi sent for comparison (Kelejnikova, in litt.). The descrip- 

 tion is very adequate for its determination. Type locality, 

 "Nouvelle-Orleans et a Mobile." 



Specimens examined. — From the following localities, 179: 



United States: Alabama (Auburn, Peterman, Tuscaloosa). Arkansas. Dela- 

 ware (Newark). District of Columbia. Florida (Bartow, Brooksville, Capron, 

 Dunedin, Enterprise, Gainesville, Haulover, Highlands Hammock State Park, 



