TAXONOMIC MORPHOLOGY 15 



In Pselaphidae the great majority of species have the abdomen with from 

 five to six visible tergites and sternites. Exceptions occur, but these are a 

 consequence of the general consolidation of the body — a family trait. Thus, 

 Cyathigerini have two visible tergites and sternites; Clavigerinae have a 

 dorsum of three fused tergites, but five to six visible sternites. In other groups 

 the number of sternites varies with sex. In such forms, unevenly distributed 

 through many tribes, the males have a ventro-terminal piece, the penial plate 

 or pygidium. This appears to be a part of the seventh visible stemite. It may 

 be excessively minute or very large and conspicuous. The penial plate may be 

 a single plate {Actium, Bibloplectus, Cedius, Cylindrarotus, Dalmosella, 

 Melba, Ramecia, Thesiastes, Thesium, Tnmioplectus , Tyrogatunus, Tyrus), 

 varying in shape from narrow-transverse, through quadrate, circular, oval, 

 semi-circular, to narrow-oblong. The penial plate may be divided into two 

 parts, a right and a left piece {Rhinoscepsis, Euplectus) . In dried specimens 

 the males of these latter show the two plates as closely appressed, the line of 

 contact being then spoken of as the longitudinal penial or pygidial carina. In 

 Euplectus, the genus can be conveniently divided into two aggregates of sub- 

 genera, depending upon whether this carina is convex to the left or to the right. 

 Again, in Sonoma tolulae the males have a seventh stemite, which is divided 

 into three pieces, a right, a left, and a median plate. 



The male genitalia and associated penial plate (Plates I, II, III) never 

 have been studied or applied to the classification of the family. This is strange 

 since the male copulatory organ (aedeagus or penis) is large, sclerotized, and 

 easily dissected in fresh or relaxed material. I have found the aedeagus to 

 offer qualitative characters in the separation of closely allied species, and to 

 give at least another criterion for the determination of generic limits as well 

 as the evolution of the family. Protected as it is from frequent contact with 

 the environment (in distinction to mouth-parts and tarsi which are in nealy 

 continual contact), and requiring close adjustment to the female genital tube 

 for successful continuance of the species, the male genital tube offers valuable 

 taxonomic characters. 



The pselaphid aedeagus is a further specialization of the staphylinoid plan. 

 It seems to be derivable from the Oxytelinae. Typically, the pselaphid aedeagus 

 consists of a large, heavily sclerotized median lobe. The basal (morpho- 

 logical anterior) part of the median lobe swells into a basal bulb. The dorsal 

 surface of the median lobe quite generally bears two membranous diaphragms, 

 the basal diaphragm is larger, usually oval, and occupies the basal half to 

 two-thirds; the apical diaphragm is smaller, oval to triangular, and occupies 

 the apical part of the median lobe. The free apical end (mor|Dhological posterior) 

 of the median lobe is generally narrowed into a sharp-pointed lamina of diverse 

 length and shape. Lateral lobes are present less frequently and are regarded 

 as primitive. These latter are usually small or membranous and may be moved 

 latero-mesiad by bilaterally symmetrical bulbar muscles of the basal bulb, or 

 these muscles may be chiefly concerned in exserting and rotating the relatively 

 large aedeagus from the male genital orifice. Occasionally the median lobe 



