8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



sclerite at the base of the palpus, their points of insertion being indi- 

 cated by the black spot on each sclerite just posterior to the hinge or 

 suture previously mentioned. 



No other muscles within the labium may be found, and with the 

 palpi as well developed as they are, it is apparent that these are 

 levators of the palpus. At least this is certainly their functional 

 significance. 



Inserted on the inner end of the barlike structure above described 

 is a pair of muscles (A, B, 2adlb). These muscles originate from 

 the tentorium, but not from its base near the posterior tentorial pits. 

 Instead the origins have migrated dorsally along the posterior arms 

 and even onto the anterior arms (B, AT). That they do originate 

 from the anterior arms, in part at least, is shown by the fact that the 

 dorsal arms {DT) of the tentorium which arise as secondary out- 

 growths of the anterior arms, are given ofif ventral to the attachment 

 of the dorsalmost fiber of this labial muscle. That the dorsal arm is 

 present is proven by the fact that the antennal muscles (MAnt) arise 

 therefrom. 



Apparently, therefore, the labium consists entirely of a prementum 

 with its appended parts, connected with the head by a membranous 

 mentum. The sclerite of the basal segment of the palpus has become 

 secondarily broken up. Whether or not the submentum is present 

 is difficult to state since from what is considered this region in closely 

 related forms (see below), there arise the adductors of the maxillary 

 stipes (A, adst), although a portion of this muscle originates also 

 from the posterior tentorial arm close to the posterior tentorial pit (pt). 



When the ventral adductors of the labium contract they cause the 

 prementum to tip outward from the head, or ventrally, with the 

 fulcrum of the lever at the margin of the head capsule. 



Carabidae (pi. 2, C). 



The labium of Harpalus sp. is separated into a well-marked pre- 

 mentum {Print), a membranous mentum {Mt), and a much narrowed 

 submentum {Smt) and gula {gu). The posterior tentorial pits {pt) 

 lie close together, just lateral to the sutures which mark off this 

 narrowed area. 



The ventral muscles of the labium consist of only one pair, the 

 ventral adductors of the labium {2adlh). They arise on the arms of 

 the posterior tentorium {Tent) and insert at the base of the pre- 

 mentum. Since the sclerotization of the mentum is lacking, these 

 muscles serve to retract the prementum. 



