10 SMITHSONIAN MISCFXLANEOUS COLLECTIONS VOL. 95 



The dorsal adductors (ladlb) have their origins on the tentorial 

 invaginations and insert on the bases of the divided prementum. Ful- 

 filling their usual role of opposing the ventral adductors, they ap- 

 parently act as levators of the combined palpus and half prementum. 



Silphidae (pi. 3, A). 



The labium of the larva of SilpJia shows for the first time, in our 

 study of the labia by families, a three-part labium, all components 

 of which are distinctly separated from the head. As in Byrrhus 

 (pi. I, D), the first prementum (pi. 3, A, IPrmt), the second pre- 

 mentum (II Print), and the postmentum (Pint) cooperate in the for- 

 mation of the three-part labium. They are set off from one another 

 by distinct membranous areas. Furthermore, the postmentum is defi- 

 nitely separated by a suture from an incipient gula (Gn). 



sup ha dift'ers from Byrrhus in that the ventral adductors of the 

 labium (2adlh) arise on the postmentum rather than on the tentorium 

 (pi. I, D). In the form studied the tentorial pits (pi. 3, A, pt) lie 

 very closely approximated and immediately behind the base of the 

 postmentum. Apparently the ventral adductor muscles have moved 

 their points of origin from the tentorial arms to the base of the post- 

 mentum. Up to this point in our consideration of the labium of the 

 various families no retractor muscles of the prementum have been 

 observed. In Silpha however these muscles (rst) are present. They 

 originate from the postmentum and insert on the base of the second 

 prementum. 



StaphyUnidae (pi. 3, B). 



The labium of Hesperus appears to consist of only two parts which 

 are distinct from the head. The submentum (Sint) is again combined 

 with the head capsule, as in the representatives of the Adephaga. It 

 differs from them however in having the submentum definitely marked 

 ofif laterally by sutures or grooves. The prementum (Print) bears the 

 palpi and a simple ligula. The mentum (Mt) is membranous almost 

 throughout but has a narrow sclerite at its base. 



There is present only one pair of ventral muscles. These, the 

 ventral adductors of the labium (2adlh), originate on the bases of 

 the tentorial arms and insert on the base of the prementum. 



Histeridac (pi. 3, C). 



In Hololepta the labium is similar to several of the preceding in 

 that it consists of a clearly marked prementum (Print) set ofif from 

 the head capsule by a membranous mentum (Mt). Also the sub- 

 mentum (Smt) is completely fused with the head capsule although 



