186 NEOTROPICAL PSELAPHIDAE 



of ten segments; (3) Third segment of the maxillary palpi transverse, sub- 

 triangular, with the external face rounded-convex and the internal face sub- 

 acute-convex or angulated; (4) Base of each elytron with two foveae; (5) 

 Distant metathoracic coxae. 



As at present constituted, the genus holds 71 species of which 13 are 

 known from the United States and Canada and 58 from the neotropics. 

 Decarthron formiceti (LeConte), distributed from Pennsylvania and New 

 Jersey south into the States bordering the Gulf of Mexico, has been designated 

 as the genotype by Bowman (1934, p. 144). 



The genus is essentially a neotropical aggregate: Mexico (18) from the 

 coastal extension of the tropical rain forest in southern Tamaulipas southward ; 

 Mexico and Guatemala (2) ; Guatemala (2) ; Panama Canal Zone (4) ; Vene- 

 zuela and Colombia (1); Colombia (2); Dutch Guiana (2); Brazil (13); 

 Peru (1); Bolivia (1); Paraguay (1); Chile (1); Argentina (8); Grenada, 

 Windward Islands (2) and Cuba (1). 



The species in general have well-developed eyes and wings and fly well, 

 coming to lights at night. This dusk flight may extend well into the night but 

 I have not found the insects active by day. Many are synoeketes within the 

 society of ants, one of the new species being adjusted to life with the rapacious 

 army ants to cite but one example. 



This is a very specialized genus of pselaphids and belongs near the 

 limits of the Brachyglutini. It has few relatives. The secondary sexual modi- 

 fications affect the male sex and may be partially outlined as follows. The 

 front of the head may be prolonged beyond the bases of the antennae into a 

 short truncated plate or into a long, conical, spiniform horn. The epistome 

 or clypeal region may be variously armed. The antennae, from the third to 

 the tenth segment, may be highly abnormal. The anterior tibiae may be dilated 

 and bear a ventral sulcus and the anterior femora may be dorsally excavated. 

 The intermediate femora are generally variously flattened and granulated or 

 excavated dorsally, the excavation being of diverse shapes and bearing spines, 

 tubercles, or contorted carinae. The posterior tibiae may be strongly inflated. 

 In contrast, the females are usually much less variable among the species, the 

 body and appendages being simple in form. For this reason the keys have 

 employed the male sex in large part and females are difficult to determine in 

 most cases. 



The following key has been modified from Raffray's group key of 1904 

 and is prepared for the male sex unless otherwise stated : 



Key to Neotropical Groups of Decarthron, Based Chiefly on Males 



Front of head prolonged anteriorly between antennal bases 2 



Front of head simply declivous or truncate between the antennal 



bases, never prolonged anteriorly 3 



2. Frontal extension in the form of a short, anteriorly truncated process 



Group XIV 



