20 ■ SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



brane, the postmentum {Pint). All signs of a gula have become ob- 

 literated. The posterior tentorial pits (pt), which at their posterior 

 ends are firmly united with the head capsule, extend into the mem- 

 branous area at the base of the labium. 



There are two pairs of ventral muscles, both of which insert on the 

 base of the prementum. The first pair, the retractors of the pre- 

 mentum (rst), originate near the posterior margin of the postmental 

 sclerite (Pmt). They lie ventral to the second pair, the ventral adduc- 

 tors of the labium {2adlb) which arise on the postoccipital ridge 

 (PoR). These latter muscles are long and slender, and their points of 

 origin have apparently migrated to their present location, possibly in 

 connection with the loss of the gular region. 



Cebrionidae (pi. 6, D). 



A study of the labium of Cebrio shows it to consist of three parts, 

 a prementum (Prmt) , a mentum {Mt), and a submentum (Smt) . The 

 prementum bears the palpi, and close behind the bases of these are 

 found three pairs of setae, the ones on either side arranged in a 

 straight line. The mentum is an elongate oval sclerite taking up the 

 central region of the labium. The submentum consists of two small, 

 triangular sclerites. They are separate from one another and located 

 near the posterior margin of the labium. 



The ventral muscles are only one pair, the ventral adductors of 

 the labium {2adlb). They arise from the triangular submental plates 

 and insert on the base of the prementum. 



Elateridae (pi. 6, H). 



The labium of the Elateridae shows externally two distinct parts, 

 the first prementum (IPrnit) and the postmentum (Pint), but upon 

 dissection there is found a third division, the second prementum 

 (IlPrmt). This latter subdivision is firmly united with the first pre- 

 mentum but is completely invaginated into the distal end of the post- 

 mentum. Between the posterior margin of the postmentum and the 

 posterior tentorial pits (pt) lie the closely approximated cardines (Cd) 

 of the maxillae. Present also is a gular region (Gu) lying between 

 and behind the tentorial pits. 



There are two pairs of ventral muscles present in the labium of 

 these larvae. The retractors of the prementum (rst) originate from 

 the distal region of the postmentum. They insert on the ventral 

 margin of the second prementum. The ventral adductors (2adlb) 

 arise from the tentorial arms (Tent) and insert on the base of the 

 first prementum. 



