NO. 13 LABIUM OF COLEOPTEROUS LARVAE ANDERSON 1 9 



Nosodendridae (pi. 6, A). 



The labium of Nosodendron consists of three clearly marked divi- 

 sions. From a study of the musclature it is seen that these are the 

 postmentum (Pint), the second prementum (IlPrmt), and the first 

 prementum (IPrmt). The first prementum carries the palpi and is 

 divided by a distinct groove almost to its base, where the groove joins 

 the apex of a definite triangular piece. The second prementum is 

 marked distally by a membranous band which separates it from the 

 first prementum. It bears near its lateral margins, slightly behind 

 the middle, obliquely directed comblike tufts of hairs. The post- 

 mentum lies behind the parts described above. It is nearly square, 

 and at its posterolateral margins are found the tentorial pits (pi). 



The ventral muscles in the labium consist of the usual two pairs, 

 the ventral adductors of the labium {2adlb) and the retractors of the 

 prementum {rst). The latter originate from the postmental sclerite, 

 approximately on a level with the internal tentorial bridge {Tent). 

 They insert on the base of the second prementum. The ventral adduc- 

 tors arise on the tentorial bar and, proceeding to their insertion at 

 the base of the first prementum, converge and nearly meet in the 

 midline at their point of attachment on the small trianglar area previ- 

 ously mentioned. 



Ptilodactylidae (pi. 6, B). 



In the labium of Ptilodactyla are found the prementum (Print), 

 a median mentum (Mt), and a proximal submentum (Smt). The 

 two latter parts together form the postmentum. The prementum bears 

 the palpi and a prominent ligula (Lig). The mentum, separated from 

 the prementum by a membranous area, is considerably broader than 

 the distal division. It is separated from the submentum by a distinct 

 suture and hinge. The latter division is firmly united with the head, 

 although it is set off from it by a suture. In connection with this 

 union it is interesting to note that the posterior tentorial pits (pt) 

 have invaded the submentum. The lateral elements of the postoccipital 

 suture have become united into a median suture (gs) and unite with 

 the ends of the posterior tentorial pits. 



Although the tentorial invaginations are located in an unusual posi- 

 tion, it is definitely assured that this posterior division is the sub- 

 mentum because from it originate the ventral adductors of the labium 

 {2adlb). They insert on the base of the prementum. 



Cantharidae (pi. 6, C). 



The labium of Chaidiognathiis shows only two parts, the terminal 

 prementum {Print) and a median oval sclerite surrounded by mem- 



