NO. 13 LABIUM OF COLEOPTEROUS LARVAE ANDERSON II 



demarcated by definite lateral grooves or sutures. The gula is narrowed 

 to the extent that the sutures which usually bound it laterally have 

 fused completely, forming a so-called gular suture (gs). 



There is only one pair of ventral muscles to be found in the labium 

 of this insect. These, the ventral adductors of the labium {2adlb), 

 originate from the posterior tentorium. They insert on the base of 

 the prementum. 



Hydrophilidae (pi. 3, D). 



The postmentum (Pint), the second prementum (I I Print), and the 

 first prementum (IPrmt) cooperate in the formation of the labium of 

 Hydrous. The first prementum bears the palpi and the Hgula (Lig). 

 The latter is smaller than in most members of this family, but it is 

 nevertheless clearly dififerentiated. The second prementum is broad, 

 and its lateral anterior margins are greatly extended. In this respect 

 it resembles the mentum of many adult beetles (pi. i, C). It is sepa- 

 rated by a well-defined membranous area from the postmentum. 

 About midway of the lateroposterior margins of the latter are found 

 the tentorial pits (pt). 



From the condition of the labium as above mentioned it would 

 be expected that there are two ventral pairs of muscles, the ventral 

 adductors of the labium (pi. 3, D, 2adlb) and the retractors of the 

 prementum (rst). The adductor muscles originate from the tentorial 

 arms near their bases, the posterior tentorial pits (pt). They con- 

 verge somewhat and insert on the base of the first prementum. The 

 retractor muscles consist of a single broad bundle in place of the more 

 usual two strands. They originate from nearly the complete posterior 

 width of the postmentum and insert along the base of the second 

 prementum. 



Languriidae (pi. 3, E). 



The labium of Languria is divided into three distinct divisions, the 

 first prementum (IPrint), the second prementum (IlPrmt), and the 

 postmentum (Pmt). Posterior to the base of the distal division is 

 the gula (Gu). The parts of the labium are separated by distinct 

 sutures but not by areas of membrane as in some forms. 



There are two pairs of ventral muscles which serve as criteria for 

 properly naming the constituents of this labium. The shorter of these, 

 the retractors of the prementum (rst), arise from the postmentum 

 and insert on the base of the second prementum. The second pair, the 

 ventral adductors of the labium (2adlb), as in Byrrhus, originate 

 from the postmentum and not from the tentorium. They insert on 

 the base of the first prementum. 



