CYDNIDAE OF THE WESTERN HEMISPHERE — FROESCHNER 423 



Distribution. — Melanaethus is restricted to the Western Hemi- 

 sphere where its members occur in the area from Maryland to Cah- 

 fornia in the north and to southern Brazil in the south. 



Discussion. — Most members of this genus have long gone under 

 the name Geotomus, but the few recently described species have been 

 assigned to Geocnetlms of Horvath. Most authors have considered 

 Melanaethvs to be a synonym of Mulsant and Key's Geotomus, for 

 which Cydnus punctulatus Costa (1847, p. 30) was designated as type 

 by Distant (1902, p. 98). From the present study and a partially 

 completed attempt to redefine the cydnid genera of the world, this 

 position appears untenable. The New World species assigned here 

 are not congeneric with Geotomus -punctulatus and can readily be sep- 

 arated from it by several features, as follows: (1) Terminal process of 

 osteolar peritreme of G. punctulatus is auriculate in shape with the 

 osteole opening near the center of its base (fig. 98), v/hile this structure 

 on American species of Melanaethus is variously convex posteriorly 

 with osteole opening posteriorly on the peritreme at the base of the 

 expansion (figs. 96, 97). (2) G. punctulatus lias nine or ten submar- 

 ginal setigerous punctures laterally on the pronotum, three or more of 

 them posterior to the transverse impression, while no species of Mela- 

 naethus possesses more than six such punctures, only one of which is 

 posterior to the transverse impression. (3) The head of G. punctula- 

 tus has a submarginal row of five to seven setigerous punctures bearing 

 long, coarse hairs, while in the forms here assigned to Melanaethus all 

 but the new species jjlanifrons has but one such puncture. Of these 

 characters, the shape of the terminal process of the osteolar peritrem.e 

 appears to be most important. 



Horvdth's genus Geocnethus, to which several American species 

 have been accredited, also has an Old World genotype, obesus Horvdth 

 (1919, p. 248), by original designation. Examination of the type of 

 Geocnethus obesus shows that it lacks a terminal modification of the 

 peritreme and so surely cannot include among its closest relatives 

 species which have a terminal modification. 



The 16 species here treated as members of Melanaethus can be ar- 

 ranged into rather distinct groups based on the extent of the osteolar 

 peritreme, as indicated by the first couplet of the key to species. 

 One group, centering around M. cavicollis (Blatchley), agrees \vith 

 the subgenus Bhytidoporus (Ehytidojjorus) in appearing to be restricted 

 to the region of the Caribbean islands with an invasion of the surround- 

 ing mainland at two points. The remainder of the species of Mela- 

 naethus are continental forms, with only two species occurring south 

 of middle Central America. 



