NO. 13 LABIUM OF COLEOPTEROUS LARVAE — ANDERSON 21 



Passalidae (pi. 6, F). 



The labium of Passalns is made up of three distinct areas : the pre- 

 mentum (Print), the mentum (Mt), and the submentum, which is 

 not separated from the gula and hence forms a combined region 

 (Gu + Smt). The prementum carries, as usual, the palpi. The men- 

 tum is triangular and devoid of setae. It lacks the typical shape as 

 found in adult beetles (pi. i, C, Mt) since its anterolateral angles are 

 not extended. There seems to be no membranous area between it and 

 the prementum but the suture separating them undoubtedly allows flexi- 

 bility. More than half the ventral surface of the labium consists of 

 the submentum. The distal part is flanked by a pair of sclerites which 

 are set off from the remainder of the region by sutures, but it is 

 doubtful if they have any significance beyond being part of the sub- 

 mentum. Slightly behind the middle and somewhat removed from the 

 lateral margins of the submentum are found the posterior tentorial 

 pits (pi. 6, F, pt), from which arise the internal tentorial bridge 

 (Tent). 



The ventral muscles are only one pair, the ventral adductors of the 

 labium (2adlh). They arise from the tentorial bridge and insert on 

 the base of the prementum. 



Scarabaeidae (pi. 6, E). 



In Ochrosidia we have a three-part labium made up of a first pre- 

 mentum which has two pairs of setae, a second prementum bearing 

 one pair of setae, and the postmentum, likewise having one pair of 

 rather large setae. The divisions are readily distinguished by a mem- 

 branous area between the first two and a flexible suture between the 

 second prementum and the postmentum. 



The ventral adductors of the labium (2adlh) arise from the ten- 

 torium (Tent) on the remnants of the posterior tentorial arms (pi. 8, 

 G, PT). They insert on the base of the first prementum (pi. 6, E, 

 IPrnit). The retractors of the prementum (rst) arise on the post- 

 mentum near the midline and insert on the base of the second pre- 

 mentum (IlPrrnt). They are slightly asymmetrical in that the right 

 muscle is considerably stouter than its fellow. This is an adapta- 

 tion, in Ochrosidia, to the unusually asymmetrical hypopharyngeal 

 sclerotization. 



Melyridae (pi. 6, G). 



The labium of Melyridae consists of a rather insignificant first 

 prementum (IPrmt), an elongate second prementum (IlPrmt), 

 and an area lying completely between the posterior tentorial pits 

 (pt) which would appear to be a combined postmentum and gula 

 (Pmt + Gu). 



