TAXONOMIC MORPHOLOGY 19 



although it may have three segments in some Goniacerini, Attapseniini; it is 

 apparently one-segmented in Arhytodini and Clavigerinae. In some pselaphids 

 (Euphalepsus) the palpus, although fully formed, is very petite (Park, 1933) 

 and nearly every segment may be grotesquely modified, often forming the 

 most reliable separation of genera (the reader is especially urged to examine 

 the palpi of neotropical Tyrini in this respect, the phylogenetic derivation of 

 which has been attempted on pp. 340-342). The neotropical Ctenistini have 

 four-segmented palpi, but some ctenistine genera [Biotus, Atinus) have two- 

 segmented palpi, while Chennium and Chenniopsis have three-segmented palpi. 

 The nature and extent of palpal modification will become apparent in the 

 following pages and needs no further elaboration here. 



In regard to number of tarsal segments the Staphylinidae is more variable 

 than the Pselaphidae. Staphylinidae may have a tarsus of three segments 

 {Micropeplus, Dinopsis, Oxytelini), four segments {Oligota, Euasthetinae), 

 anterior and intennediate with four and posterior tarsi with five (Bolitocharini) , 

 anterior with four, intermediate and posterior with five (Myrmedoniini), five 

 segments (Aleocharini, Paederinae, Steninae). The Pselaphidae have three- 

 segmented tarsi, with the exception of the Dimerini which has two-segmented 

 tarsi. The Dimerini, however, holds but a single species, Dimerus staphy- 

 linoides Fiori of Italy. 



The pselaphid tarsus is generally primitive, the chief variation being in 

 the relative size of the three tarsomeres. Two tribes have very specialized 

 tarsi: the third tarsomere is bilobed in the Schistodactylini and the second 

 tarsomere is bilobed in the Arhytodini. There is some sexual differentiation in 

 the tarsus. Thus the males of certain brachyglutines {Braxyda, Bryaxina, 

 Xybaris, Achillia) have the second anterior tarsomere laterally dilated, dorso- 

 ventrally flattened, and bearing a pad of setae on the ventral surface. Xybarida 

 nasicola has the second tarsomere relatively shorter and thicker on the anterior 

 tarsi than this segment of the other tarsi, and bears on the ventrally flattened 

 face stiff setae in the male sex. The female of this species has the normally 

 slender, unsetose tarsi. On the other hand both sexes of Raxyhis have the sec- 

 ond tarsomere of the anterior tarsi thicker than the third, and ventrally clothed 

 with long setae. There is considerable variation in the tarsal claws. In general 

 there may be a single claw, two unequally developed claws, or two equally de- 

 veloped claws, and this variation is discussed at length elsewhere. 



Thus we may generalize by saying that the number of visible abdominal 

 segments and the number of tarsomeres are relatively variable in staphy- 

 linids and conservative in pselaphids; the maxillary palpi are variable in 

 pselaphids and conservative in staphylinids. 



Relatively speaking, the antennae are also conservative in staphylinids 

 and notably variable in pselaphids. These appendages vie with the maxillary 

 palpi in extent of modification; they are more variable in pselaphids than in 

 any other family of beetles, with the possible exception of the Paussidae. They 

 range from two to eleven segments, and practically any antennomere can bear 

 sulci, foveae, spines or teeth, peculiar pubescence or specialized appendages. 



