14 NEOTROPICAL P3ELAPHIDAE 



Island, Gatun Lake, in the Panama Canal Zone, to be discussed at length in 

 this report, this artificially isolated mountain peak of only a few square miles 

 yielded 44 species on three expeditions, and of this number 40 were new. From 

 these few instances it will be seen that the pselaphids of the American tropics 

 are incompletely known. 



There is no single, qualitative criterion the application of which will 

 separate all pselaphids from all staphylinids. Such a condition is the rule in 

 studies on classification and is to be expected if we consider the species as 

 by-products of the evolutionary process. 



It is apparent that Pselaphidae are highly evolved staphylinoid beetles 

 in which certain structural parts have attained a peculiar degree of speciali- 

 zation, presumably through a differential selection by the environment of genetic 

 combinations over a long period of time. Genetically, nothing is known of the 

 stability or lability of pselaphid structure and function. Therefore we may 

 not check the validity of a pselaphid species by experimental breeding, nor 

 map out the probable lines of taxonomic development with the degree of as- 

 surance done for the Drosophilidae (cf. Dobzhansky, 1937) or the Cynipidae 

 (Kinsey, 1936). Classification of Pselaphidae, then, must depend upon com- 

 parative anatomy (without the aid of comparative embryology) and the 

 ecological science of zoogeography. 



The pselaphids are wholly brachyelytrous, the mesothoracic wings or 

 elytra being short and exposing part of the abdomen. This condition is shared 

 by other families, for example the Staphylinidae, part of Ptiliidae, et cetera. 



Their size range is intermediate between staphylinids and ptiliids. The 

 largest pselaphid known to me is the Brazilian Hamotus (Hamotoides) 

 ecitophilus Raffray. This giant measures 5.5 millimeters in length and lives 

 in the society of Eciton army ants. A number of species are small, measuring 

 0.5 to 0.7 millimeter. The average length for the family is about 1.5 millimeters. 



Pselaphidae have a more compact body plan than Staphylinidae. This 

 is one of the best criteria for separating the two families. In pselaphids the 

 head capsule is more solid, and the gular sutures, so well shown in Paederinae, 

 are absent or reduced. Secondly, this consolidation is shown in the prothorax, 

 where the lateral sclerites are generally shorter and of a more rigid con- 

 struction than in Staphylinidae. Staphylinids generally have six visible ster- 

 nites (morphologically segments III to VIII). According to Leng (1920) some 

 variation occurs, for example five segments {Micropeplus, Oligota), six seg- 

 ments (Euaesthetus) , seven segments (Oxytelini, Aleocharini) and eight seg- 

 ments visible and movable (Omalium). Blackwelder (1936) gives the total 

 number of abdominal segments in Staphylinidae as ten, of which the first is 

 represented by tergite; second by tergite usually and sternite in some species; 

 third, fourth, fifth, sixth, seventh and eight with normal tergite and sternite; 

 ninth and tenth segments variously modified and often considered with the 

 genitalia. 



