NO. 13 STAPHYLINIDAE BLACKWELDER 9 



interpretation of Tanner (1927). He has considered only one staphy- 

 linid, Creophilus villosus. 



The spiracles are the chief landmarks of the abdomen. They occur 

 on each segment from one to eight. They are in all insects morpho- 

 logically a part of the tergum and in these forms are generally actually 

 in the tergites. A curious error is made regarding these by Leconte 

 and Horn (1883), as follows: "The breathing pores, or spiracles. 

 are situated in the connecting membranes, or in the upper inflexed 

 portions of the ventral segments." In the present family, at least, 

 they are always very definitely placed in the tergal elements. 



Structure of a Representative Species 



The species Creophilus villosus (Grav.) has been selected to be 

 the subject of detailed investigation for the following reasons: It is 

 one of the commonest, most widespread, and most readily attainable 

 of American staphylinids ; it very closely resembles related species 

 that are common throughout most of the world ; it is a typical staphy- 

 linid, being very similar to the type genus of the family ; and it has 

 been used, more than any other staphylinid species, as the basis for 

 previous studies of the morphology of this family. 



THE head 



The walls of the head are continuously heavily sclerotized on the 

 dorsal, lateral, and ventral aspects. These walls thus form a solid 

 capsule (fig. I F) with an opening at the posterior end, the foramen 

 magnum. The walls of this capsule are formed of certain sclerites 

 which have become united, with a corresponding obliteration of the 

 sutures between them. 



The dorsal aspect of the head (fig. i A) is occupied by a single 

 large sclerite extending anteriorly from the rim of the foramen mag- 

 num (for) to the membranous anteclypeus (aclp) and occupying the 

 entire width of the head. This area is the epicranium (epi) and is 

 formed by the obliteration of sutures which would divide it into frons, 

 vertex, genae, postgenae, and occiput. The occiput (oc) is represented 

 by a narrow band around the dorsal and lateral rims of the foramen 

 magnum, but it is undifferentiated from the vertex (z'.r). This is 

 due to the obliteration of the occipital suture. The ventral continua- 

 tions of the occiput on the sides of the head are the postgenae 

 (fig. I A, E, pge). Since the occipital sutures, if present, would ex- 

 tend to the base of the labium and maxillae, it follows that the areas 

 included by them, the postgenae, occupy in this species the two regions 



