NO. 13 STAPHYLINIDAE BLACKWELDER 7I 



but the series shows the range from the long slender types of Meto- 

 poncus and Tanyrhinus to the short transverse one of Liparocephalus. 



The extent of deflection of the sides of the elytra depends in great 

 part on the convexity of the thorax. In many species this area is rather 

 abruptly deflexed and of considerable size (figs. 24D, F, K). This 

 area has frequently been called the epipleurae, but if this term be 

 used, it should be borne in mind that it is a convenient name for a 

 region rather than for a definite morphological unit. The epipleuron 

 is occasionally separated from the discal portion of the elytron by 

 a raised line as in Bled ins (fig. 24 I) and Tanyrhinus (fig. 24 B). The 

 epipleuron may bear a distinct line parallel to the outer margin. This 

 is called the pleural fold by Casey but is more properly termed the 

 epipleural fold, although its exact significance is not known. 



In most of the Xantholinini, such as Metoponcus and Xantholinus, 

 the so-called elytral suture or median edge of the elytron is some- 

 what abnormal. The thickness of the elytron along this edge is 

 gradually diminished so^ that the whole edge appears to be beveled. 

 This beveled surface is smooth and unclothed and usually less heavily 

 pigmented than the rest of the elytron. These two edges overlap one 

 another when the elytra are at rest. No special morphological sig- 

 nificance is attributed to this feature as it is only a slight modification 

 of the normal suture. 



The structure of the sterna of the mesothorax and metathorax is 

 influenced to a large extent by the size, shape, and position of the coxal 

 cavities of the mesothorax. The actual points of insertion of the coxae 

 may be widely separated (fig. 25 C) or close together (fig. 25 B) 

 without changing the relation of the parts. In these two examples 

 the more widely separated ones are still confluent on the midline, 

 whereas the approximate ones are separated by the two sternal 

 processes. 



It should be understood that in speaking of the coxal cavities, one 

 is referring to the entire depression occupied by the coxae. This de- 

 pression is bounded anteriorly by the mesosternum and generally is 

 set off posteriorly by a line on the metasternum. The floor of this 

 depression is made up of the deflexed portions of the mesosterna and 

 metasterna, and it is generally more or less elevated in the middle to 

 form a ridge between the two coxal cavities. However, unless the 

 actual surface of the two sterna meet on the midline or are closely 

 approximated, the cavities are considered to be confluent. The pos- 

 terior border of the two cavities is usually marked by a line which 

 is common to both and delimits anteriorly the process of the 

 metasternum. 



