NO. 13 LABIUM OF COLEOPTEROUS LARVAE ANDERSON I7 



Their points of insertion are noticeable from the exterior as small 

 ovals more heavily sclerotizecl than the surrounding integument. The 

 ventral adductors of the labium {sadlh) arise from the postmental 

 sclerite and insert on the base of the first prementum. 



Alleculidae (pi. 5, E). 



The first and the second prementum, in this labium, are clearly- 

 marked off from each other by a membranous area. The second pre- 

 mentum (IlPrmt) is likewise set off from the postmentum (Pmt) 

 by a membrane. The postmentum has as its posterior limit an imagi- 

 nary line connecting the posterior tentorial pits (pt). Behind the 

 postmentum, but in no way marked off from it, is the gula (Git). The 

 latter is bounded along the sides by faint indications of the postoccipital 

 suture. 



The ventral muscles again consist of two pairs. The ventral adduc- 

 tors of the labium {2adlh) originate on the tentorium {Tent) and 

 insert on the first prementum (IPrmt). The retractors of the pre- 

 mentum (rst) arise on the postmentmn slightly anterior to the ten- 

 torial pits and insert on the base of the second prementum. 



Tenebrionidae (pi. 5, C). 



The divisions of the labium of Merinus are consistent with the 

 basic scheme of the three-part labium of coleopterous larvae. The gula 

 is definitely separated from the postmentum (Pint) by a suture. It 

 is marked laterally by the posterior tentorial pits (pt) and the postocci- 

 pital suture (pos) and posteriorly by the ventral margin of the 

 postoccipital ridge (PoR). 



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

 torial arms (Tent) and insert on the base of the first prementum. 

 The usually paired retractors of the prementum (rst) are united in 

 this species into a comparatively large median bundle which arises 

 from the posterior margin of the postmentum. It inserts on the base 

 of the second prementum. 



Lagriidae (pi. 5, F). 



There are seen in the representative of this family the usual three 

 divisions of the labium, the postmentum (Pint), the second prementum 

 (I I Print), and the first prementum (I Print). The first prementum 

 carries the palpi and a distinct ligula. The second prementum is sepa- 

 rated from the preceding subdivision by a membranous strip. The 

 postmentum, lying behind the second prementum, is separated from 

 the latter by a distinct membranous area. The lateral margins of the 

 postmentum diverge toward the proximal margin. 



