NO. 13 STAPH YLINIDAE BLACK WELDER 55 



determined only by following the anterior tentorial arms to their 

 anterior extremity. 



The ends of the dorsal arms of the tentorium are likewise invisible 

 from the exterior in unprepared specimens. By following the dorsal 

 arms the point of insertion is determined. This point is indicated in 

 the figures by a tiny circle of dots, and it is found on the vertex gen- 

 erally between the eyes, one on each side of the center. In many species 

 the dorsal arms apparently do not reach the vertex. These include 

 Acylophorus (fig. ii G), Oxyporus (fig. ii D), Hypocyptus (fig. 

 10 D), Tachyporus (fig. lo C), Bolitob'ms (fig. ii F), Xcnoditsa (fig. 

 10 K), Lorinota (fig. lo L), etc. 



The ventral aspect of the head, similarly to the dorsal, is consider- 

 ably modified by the obliteration of sutures and the consequent fusion 

 of primitive elements. The vertex extends around behind the eyes 

 and is continuous with the genae, if present, and sometimes with the 

 median gular area and the postgenal area. 



In the forms already listed as possessing an occipital suture, the 

 vertex is separated by it from the occiput and to a greater or less 

 extent from the postgenae, which are continuous with the occiput. 

 Where no occipital suture is present the vertex, occiput, and post- 

 genae are all united to form the epicranium. The postoccipital sutures 

 are said to be the most constant of all the head sutures. However, 

 this suture is not evident on any of these species (except possibly 

 Philonthns, fig. 12 J) until it reaches the ventral side of the head and 

 becomes the gular sutures. 



The gular sutures are formed by the relative anterior migration of 

 the posterior tentorial pits and normally extend from the foramen 

 magnum to the base of the labium, separating the ventral aspect into 

 three parts. Enclosed between these sutures is a sclerite known as the 

 gula. Stickney states that it is always complete in the Staphylinidae, 

 but even under the present interpretation the additional material proves 

 the contrary to be the case. The gula may be considered to be com- 

 plete when it extends from the foramen magnum to the tentorial 

 pits, where it unites with the submentum. 



The gula has been found to be incomplete in 13 of the species used 

 in this study. Three types of conditions are found among these 13. 

 In some the gula is separated from the pits by the meeting of the gular 

 sutures on the midline, as in Leptochirus, Bledius, Osorius, Gastro- 

 lobiuin, Stilicus, Asteniis (fig. 12 B), Xantholinus, Staphylinus, and 

 Cafius. Some have the gular sutures incomplete posteriorly, such as 

 Paederillus, Lathrotropis, and Trachysectiis. One species, Metoponcus 

 (fig. 12 I), shows no sign of the gular sutures at all; the posterior 



