NO. 13 LABIUM OF COLEOPTEROUS LARVAE ANDERSON 1 3 



the middle, and a smaller pair located near the posterolateral margins. 

 The postmentum (Pint) is marked laterally by the posterior tentorial 

 pits (pt) and posteriorly by the ventral margin of the foramen. 



The ventral adductors of the labium {2adlh) arise on the cross bar 

 or bridge of the tentorium and insert on the base of the first pre- 

 mentum. The retractors of the prementum {rst) arise on the proximal 

 part of the postmental area and insert on the base of the second 

 prementum. 



Nitidulidae (pi. 4, A). 



The labium of this family is made up of three divisions, only one 

 of which belongs to the prementum. The posterior two parts are 

 subdivisions of the postmentum. The prementum (Print) bears one 

 pair of setae which arise from the rather distinctly shaped sclerite 

 of the prementum. It also carries the palpi which consist of only 

 one segment in contrast to the usual condition of two segments. The 

 mentum (Mt) is separated from the preceding division by a com- 

 paratively broad membranous area. It bears one pair of large setae. 

 In the species figured the mentum and submentum (Smt) are sepa- 

 rated by a weakly indicated groove, but in other species of the family 

 the separation is very clearly marked (Boving and Craighead, 1930, 

 pi. 35, fig. B). The submentum has a rather peculiar urn shape and 

 extends to the posterior margin of the head. 



There is only one pair of ventral muscles in the labium. The lateral 

 elements of this muscle, the ventral adductors of the labium (2adlb), 

 at their point of origin, unite in the midline of the submentum and 

 diverge slightly to their insertion on the sclerite at the base of the 

 prementum. 



Endomychidae (pi. 4, B). 



The labium of Endomychidae shows two divisions, the prementum 

 (Prmt) and the postmentum (Pint). The prementum bears the palpi 

 and a short ligula. It also has on its ventral surface a pair of setae 

 which are situated slightly proximal to the bases of the palpi. The 

 postmentum (Pint) extends posteriorly to the neck membrane and 

 makes up the larger portion of the labium. On it are located two pairs 

 of setae and an unpaired median seta near the distal margin. Bounding 

 the postmentum on its posterolateral margins are the posterior ten- 

 torial pits (pt). 



The ventral muscles, as would be expected, are only one pair, the 

 ventral adductors of the labium (2adlb). They originate on the ten- 

 torium (Tent) and proceed obliquely from their points of origin to 

 insert on the base of the prementum, where they nearly meet in the 

 midline. 



