NO. 13 STAPH YLINIDAE BLACK WELDER 73 



The most common situation in this family is for the two cavities 

 to be confluent on the micUine. That is, the processes from the meso- 

 thorax and metathorax do not meet. In nearly all cases, however, the 

 mesothoracic process projects more or less between the coxae. This 

 group includes Geodromicus, Pelecomalhmi, Lathrimaeum, Proteiniis, 

 Eumahis, Pseudopsis, Bledius, Oxytelus, Aploderus, Osorius, all the 

 Paederinae, Metoponcus (fig. 25 C), all the Staphylinini (fig. 25 A), 

 Xanthopygini, and Quediini, Habrocerus, and LiparocepMlus. 



In Stenus, Hypocyptus (fig. 25 D), and Aleochara the mesothoracic 

 process attains the metasternum, thereby separating the coxal cavities 

 without the aid of a metathoracic process. 



This situation is just reversed in Platystcthus and Oxyporus (fig. 

 25 E), in which the metathoracic process attains the mesosternum and 

 separates the cavities. 



Frequently, however, the two processes meet midway and take 

 equal part in the separation. In this group are the following species : 

 Micropeplus, Leptochirus (fig. 25 B), Trigonurus, Phloeocharis, 

 Tachyporus, Tachinus, Erchomns, Bolitohius, Oligota, Xenodusa, 

 Larinofa, and Baryodma. 



The mesosternum is usually very short and not separated from the 

 pleural areas. Considerable reduction has taken place in some of 

 the pleural sclerites, but in some species they are distinct and separate. 



The metasternum may be very short and transverse as in Hypo- 

 cyptus (fig. 25 D) or rather elongate as in Metoponcus (fig. 25 C). 

 In general it is deflexed anteriorly to form most of the floor of the 

 coxal cavities, but in Metoponcus this part is formed by the inflexed 

 portion of the mesosternum, and the metasternum has a narrow 

 emargination at the middle which receives a slender process of the 

 mesosternum. 



The metasternum is always completely separated from the meta- 

 pleurites. It is variously emarginate posteriorly to fit the coxae of 

 the metathoracic legs, and generally shows the articulations of the 

 coxae at the middle. 



THE LEGS 



The greater part of the large amount of variation in the legs is due 

 to the relative sizes of the parts rather than to any fundamental differ- 

 ences in structure. The presence or absence of calcaria or other 

 setae and the variation in number of tarsal subsegments or tarsomeres 

 constitute the principal structural differences. 



