EUPLECTINI 65 



The abdomen is generally elongate, strongly margined, and of five to six 

 visible tergites ; ventrally there may be six visible stemites in both sexes, or six 

 in the females and seven in the males. In the latter case, the seventh stemite 

 may be in one piece, or longitudinally divided into a right and a left pygidial 

 plate. The male sex often has the sternites secondarily modified. 



Euplectini offer a promising field for evolutionary study. Such an investi- 

 gation is not contemplated in the present paper, since the world fauna must be 

 taken into such calculations. The American euplectines appear to culminate in 

 the cluster of genera which includes Melba, Dalmosella, Basolum, Pseudo- 

 trimium, Trimiomelba, Actium, Actinoma, Trimiosella and their allies. In these 

 genera there is a general summation of morphological features away from the 

 staphylinid pattern. This is suggested by increasing glabrosity, consolidation 

 of sternal sutures and foveae, increasing prominence of the distal antennal seg- 

 ment, and in many of these genera the signal development of specialized capit- 

 ulate setae on the ventral surface of the head. These trimiforms or melbaforms 

 appear to have affinities with some of the Brachyglutini, for example Eupsenius 

 and Eupsenina. 



If the assumption is made that pselaphids have evolved from staphylinoid 

 ancestors, and morphological evidence has been presented for such a view, then 

 development in the euplectines must be based on more and more remote organ- 

 ization from the staphylinid stem. For example, the following criteria may be 

 taken into brief consideration: 



1. General consolidation of the body, including head, thorax and abdomen, 

 is considered a specialization of great weight, carrying the family from Staphy- 

 linidae, through Faronini, into Clavigerinae. Such consolidation leads to increas- 

 ing abdominal immobility, loss of sutures, reduction of sternal foveae and 

 finally loss of sternal foveae. 



2. A general vestiture of simple setae is considered primitive, but either 

 a glabrous condition, or highly modified setae such as capitulate or scales, or 

 a combination of glabrosity with modified setae, is considered specialized. 



3. Tarsi with two equal, simple claws are considered generalized. Bilater- 

 ally asymmetrical claws, reduction in the size of one claw, or presence of a 

 single claw are considered progressively specialized. 



4. Tendency towards filiform or moniliform antennae with a loose weakly 

 developed club is considered primitive, but the development of a large antennal 

 club and the progressively larger distal segment of the club, is considered 

 specialized. 



5. Simple four-segmented maxillary palpi are primitive, whereas increas- 

 ing specialization of the palpi is viewed as more highly evolved. 



6. A penial plate, increasing the number of visible sternites in the male 

 sex to seven, is more primitive than six sternites visible. Where this plate is 

 longitudinally divided into a right and left piece by the pygidial carina, the 

 combination is more primitive than a single penial plate. This single penial plate 

 may move asymmetrically to the right, or to the left. 



7. The bilaterally symmetrical aedeagus, with lateral lobes, is more primi- 

 tive than the asymmetrical aedeagus, with fewer parts. 



