18 NEOTROPICAL PSELAPHIDAE 



The fourth, fifth, sixth, seventh, and eighth sternites are usually visible, and 

 are commonly termed the ventral abdominal segments. The ninth and tenth 

 segments are involved in the genitalia. 



Therefore the pselaphid abdomen shows evidence for ten segments, but 

 the strongly sclerotized, normally visible segments are five to six dorsals and 

 ventrals, plus the pygidial plate in some males and some females. In the de- 

 scriptions of species {vide infra) these visible segments are counted from the 

 base of the abdomen apically, and their exact tergite and sternite origin is 

 not counted, unless specifically mentioned. Thus the "first abdominal seg- 

 ment" refers to the first visible segment, the "second ventral segment" refers 

 to the second ventrally visible segment, et cetera. 



A physiological character, that of movability of the abdominal segments, 

 has been made the most of in separating the two families. This can be utilized, 

 however, with living material or relaxed specimens, and is relative. Thus within 

 the Staphylinidae some groups (Staphylininae, Aleocharinae, Paederinae) have 

 a highly mobile abdomen, and may carry the apex elevated or move it dorso- 

 ventrally in the typical staphylinid gesture; in Steninae this is not so greatly 

 developed as a rule; in the Trilobitideini, a tribe of staphylinids created by 

 Fauvel to hold the species Trilobitideus mirabilis, the abdominal segments are 

 said to be (Raffray, 1908) solidly immovable in appearance, although more 

 or less mobile in the living state. In the Pselaphidae the movability of the 

 abdomen is generally much less, and is antero-posterior in nature (retractile) 

 rather than freely movable in the dorso-ventral plane; however, this is also 

 relative. Thus the Clavigerinae have practicaly no abdominal movement; the 

 Tyrini and Batrisini are more intermediate in this respect; certain Euplectini 

 (the New Zealand Eleusomatus) have an abnormal abdomen for pselaphids, 

 constructed in general on the staphylinid plan: the abdomen is gradually and 

 strongly tapered posteriorly. In Eleusomatus the males have six sternites and 

 the females only five visible. The abdomen in this, and other euplectine genera, 

 as well as Sonoma among Faronini, may be as movable as that of some of the 

 staphylinids. 



When everything is considered, however, this mobility of the abdomen 

 and the structural differences which make it possible or impossible, is one of 

 the most important criteria for separating the two families under discussion. 



The Pselaphidae have the labial palpi either two-segmented (Pselaphinae) 

 or one-segmented (Clavigerinae). The Staphylinidae generally have three- 

 segmented labial palpi. 



The Pselaphidae nearly always have the distal segment of the maxillary 

 palpi provided with an apical or subapical palpal cone; this structure is gen- 

 erally lacking in Staphylinidae. In general it may be said that Staphylinidae 

 have remarkably conservative maxillary palpi, usually four-segmented and 

 filiform although exceptions are known. On the other hand, Pselaphidae have 

 the most variable maxillary palpi known to the author, in fact the name of 

 the genus Pselaphus is derived from the Greek ("I feel my way") and refers 

 to these remarkable organs. The pselaphid palpus is usually four-segmented, 



