TAXONOMIC MORPHOLOGY 17 



no Batrisodes has a primitive aedeagus. This is a genus where reduction of parts 

 is strikingly developed. 



Overlaid upon this superficial simplicity is a developing asymmetry. 

 Thus Batrisodes furcatus and riparius are bilaterally symmetrical while 

 globosus, denticollis and schaumi are progressively asymmetrical. The species 

 of this genus studied so far culminate in the aberrant monstrosus. In this latter 

 species the asymmetry is extreme and an accessory piece is developed. The 

 aedeagus of monstrosus is so far removed that it should serve to divide the 

 genus into two subgenera. 



The Tyrini appear to have a very specialized penis, with some features 

 common to Batrisini and Ctenistini but little affinity with Brachyglutini and 

 Tychini. Among tyrines studies, Ceophyllus and Tmesiphorus are relatively 

 primitive, with reduced but symmetrical aedeagus; Tyrus is more specialized 

 in its pronounced asymmetry, but the presence of the penial plate is a primitive 

 feature; the system appears to culminate, thus far, in Cedius. In this latter 

 genus there is an extreme asymmetry which is directly correlated with the 

 penial plate. Thus in Cedius ziegleri the asymmetry is to the left and there 

 is a sinistral penial plat€ ; in spinosus the asymmetry is to the right and there 

 is a dextral penial plate. 



The Clavigerinae {Fustiger veracruzensis) have an aedeagus which pre- 

 sents no novelties from the tyrine type, being apparently homologous with the 

 bilaterally symmetrical organ of Ceophyllus. This is further important evidence 

 in support of not more than subfamily rank for these symphilic pselaphids. 



Contrary to most systems of classification, the Euplectini and Trichony- 

 chini are highly specialized as regards the aedeagus. The two genera studied 

 {Rhexidius and Dalmosella) have highly complex, asymmetrical male genitalia 

 — much less oxyteline than the brachyglutine aedeagus. Enough has been said 

 here, in this preliminary study, to demonstrate the importance of male genitalia 

 in the taxonomy of the family. A complete evaluation must await the study 

 of more genera. 



The pselaphid abdomen apparently consists of ten segments, which agrees 

 with the opinion of Blackwelder for staphylinids, and of Tanner (1927) for 

 beetles in general. The first and second tergites are either wholly membranous, 

 or slightly sclerotized and more or less folded. The third tergite is usually 

 sclerotized. The first three tergites are generally not visible in dried specimens, 

 being retracted and hidden beneath the elytra in the living condition and re- 

 maining so nidden unless potashed preparations are made. The fourth, fifth, 

 sixth, seventh, and eighth are visible and are commonly termed the first to 

 the fifth dorsal segments; the third tergite may be visible, in which case siy 

 dorsal abdominal segments can be counted. 



The first sternite is apparently absent as a general rule; the second ster- 

 nite is present as a membranous area articulating the metastemum to the third 

 sternite, and continuous with the membranous second tergite. The third sternite 

 may or may not be visible; if visible it is sclerotized and may be wholly 

 visible, or visible as a variously modified area between the posterior coxae. 



