TAXONOMIC MORPHOLOGY 23 



terum characteristically reduced between the coxae, so that the anterior coxal 

 cavities are large, confluent and opened posteriorly; the anterior coxae are 

 typically large, subconical and either contiguous or narrowly separated. 



The mesosternum is characteristically short and wide. Anteriad of the coxal 

 cavities, it presents a highly diverse appearance of great convenience in sepa- 

 rating genera ; this variation can be appreciated only through concentrated com- 

 parative study. As in most beetles, the median portion of the ventral surface of 

 the mesothorax is composed of the unpaired mesosternum, usually wider than 

 long and in a varying degree bounding the coxal cavities posteriorly. It projects 

 in a varying degree between the coxal cavities as the mesostemal process. Lat- 

 erally the mesosternum is bounded by the epistemum. When the mesosternum 

 and epistemum are clearly separated, the dividing suture is the stemopleural 

 suture, but there is a varying degree of fusion between the two sclerites, this 

 line of fusion being marked at times by carinae or foveae. Similarly, the 

 epimeron may be present at a distinct sclerite ventrally, or may not be apparent 

 as a discrete element. Anteriorly the mesosternum presents a system of foveae, 

 carinae, ornamented depressions or pubescent areas which make this part of 

 the pselaphid body very different in appearance from the homologous region of 

 the staphylinid. The anteriorly narrowed, "neck-like" portion of the mesosternal 

 area articulates with the prothorax by a folded, extensive membrane ; and where 

 this membrane attaches to the mesosternum and mesoepistemum this region of 

 the sternum is elevated generally into a heavily sclerotized collar. This collar 

 may represent the prepectus of staphylinids, and for convenience here is termed 

 the prepectoid area. Since the prepectoid is discussed and figured, no more need 

 be said here save that often it is secondarily depressed or modified to hold the 

 tips of the reposed anterior coxae. The mesothoracic coxal cavities are large, 

 rounded, closed posteriorly by the metasternum, and are wholly confluent, 

 slightly confluent, narrowly separated by the intercoxal lamella, composed of 

 mesosternal and metastemal processes, or finally may be widely separated. The 

 coxae are, therefore, contiguous to separated and moderately distant as in 

 Adranes, for example. 



The metasternum is characteristically large. It is often modified by tu- 

 bercles, spines, teeth, carinae, sulci and foveae. Such elaborations present both 

 specific and sexual differences and are consequently of great use in identifica- 

 tion. For example the males of Adranes have the metasternum greatly modified 

 by spines or spinoid tubercles in contrast to the females. This modification 

 reached a peak in Arhytodini where the males may have a pair of tubercles, or 

 a pair of small sharp, hooked spines, or both tubercles and spines in various 

 stages of development and position while the females have a simple metastemal 

 field. On the other hand both males and females of some Neotyrus, Tyrogatunus 

 and other genera have similarly modified metasteraa. 



Degree of separation of the intermediate coxae is variable, and of impor- 

 tance in tribal separation. Thus Clavigerinae, Pselaphini, Batrisini and Brachy- 

 glutini have the coxae usually well separated, but the last mentioned tribe 

 shows several degrees of separation and hence groups of brachyglutine genera 



