NO. 13 LABIUM OF COLEOPTEROUS LARVAE ANDERSON 7 



The dorsal adductors (ladlb) are typical in so far as their insertion 

 is concerned, since they attach on the first prementum. Their point 

 of origin, however, shows considerable divergence, since they arise, 

 not from the tentorial bar but from the internal surface of the post- 

 mentum, near the point of origin of the retractors of the prementum. 



That Byrrhus is not alone in having muscles other than the retrac- 

 tors of the prementum arising from the postmentum is shown by 

 several outstanding examples, among which are Pytho sp. (pi, 5, D), 

 Lagriidae (pi. 5, F), Cucujus davipes (pi. 3, F), and Langnria laeta 

 (pi. 3, E). Such findings are in direct contradiction to the statement 

 of Snodgrass (1935, p. 149), and to make the facts agree we must 

 consider that the origins of muscles may migrate to a certain degree. 

 It is to be noted, however, that except in very unusual cases of migra- 

 tion (Chauliognathns, pi. 6, C) the muscular origins have not moved 

 very far. In most cases when the point of origin is on the post- 

 mentum, it is directly ventral to the tentorial bar which extends across 

 the head between the tentorial pits, as shown in Byrrhus (pi. i, D). 



II. DESCRIPTIONS OF LABIA OF COLEOPTEROUS LARVAE 

 CicindeUdae^ (pi. 2, A, B). 



The labium of Cicindela sp. is made up of a rather compact and 

 firmly united prementum (A, Print) attached to the head capsule 

 by a membranous area, which, as in other representatives of the 

 Adephaga, is called the mentum (Mt). The submentum (Smt), if it 

 should be considered as being present, has lost what membranous con- 

 nection it may have had with the head capsule and is inseparably 

 united with the ventral wall of the head. 



At the base of each palpus (Pip) in the species studied there is a 

 small sclerotic area divided by a suture, which acts as a hinge. This 

 sclerite is in very close union with the palpus and also with the basal 

 sclerite of the prementum, which partially surrounds it at the base 

 and extends forward, as a bar, beyond the bases of the palpi. The 

 latter sclerite stops at the margin of the head capsule to which it is 

 connected by the membranous mentum, but the above-mentioned bar 

 extends posteriorly into the head for some distance. Thus we must 

 consider the bar as a continuation of the basal sclerite of the 

 prementum. 



Two bundles of muscle fibers (A, B, Iplp), one on either side, 

 arise from this bar, within the head capsule. They insert on the 



^ The families of Coleoptera have been arranged in the systematic order of 

 Boving and Craighead (1930, pp. 70-80). 



