NO. 13 LABIUM OF COLEOPTEROUS LARVAE — ANDERSON 15 



The ventral adductors of the labium {2adlb) arise from the tentorial 

 bridge {Tent) and insert at the base of the first prementum. 



Colydiidae (pi. 4, G). 



The labium of the representative of the family Colydiidae shows 

 no departure from the customary structure of this group. The usual 

 three divisions are clearly marked and readily interpreted from a 

 study of the musculature. The first prementum (I Print) bears the 

 palpi and in addition two pairs of setae, the proximal pair much 

 shorter than the distal pair. The second prementum (IlPrmt) like- 

 wise carries two pairs of setae. It is separated by membranous areas 

 from the first prementum distally, and from the postmentum {Pint) 

 proximally. The latter bears, near its anterior margin, two pairs of 

 setae, the distal pair of which is exceptionally long and slender. The 

 lateroposterior margins are marked by the posterior tentorial pits {pt). 



There are two pairs of ventral labial muscles, neither of which 

 presents any unusual features. The ventral adductors of the labium 

 {2adlb) originate from the tentorial bridge {Tent) and insert on the 

 base of the first prementum. The retractors of the prementum {rst) 

 arise from the posterior region of the postmentum and insert on the 

 base of the second prementum. 



Mycetophagidae (pi. 4, C). 



The prementum of Mycetophagus is subdivided into the first pre- 

 mentum {I Print) and the second prementum {I I Print). Each of 

 these divisions bears one pair of setae and is separated from the 

 other by a membranous area. The second prementum is set off from 

 the postmentum {Pint) by a second area of membrane. The post- 

 mentum has one pair of. setae, located slightly before and mesal to the 

 anterior ends of the tentorial pits {pt). There is a slight indication 

 of a groove or suture (indicated in the figure by a broken line) which 

 connects the anterior ends of the tentorial pits. This may be a rudi- 

 ment of a previously well-marked boundary line between the post- 

 mentum and the gula {Gu). This is quite possible because of the 

 fact that the retractors of the prementum originate on the postmentum 

 just anterior to this line. 



The ventral adductors of the labium {2adlh) have their origin on 

 the tentorium {Tent) and insert on the base of the first prementum. 

 The retractors of the prementum {rst) arise from the posterolateral 

 portion of the postmentum and insert on the base of the second 

 prementum. 



Synchroidae (pi. 5, A). 



The first prementum {IPrmf), which is clearly set off from the 

 second prementum by membrane, bears a pair of setae situated just 



