l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



behind the bases of the palpi. The ligula is rather more enlarged than 

 ordinarily, and it has a considerable group of sensory setae distributed 

 on its distal portion. The second prementum (IlPrmt) has two pairs 

 of setae located close to the lateral margins about midway from the 

 distal to the proximal boundary. The postmentum {Pint) is sepa- 

 rated anteriorly from the prementum by a suture and is interpreted 

 as extending to the posterior margin of the head. The proximal 

 portion of the postmentum lies between the tentorial pits {pt) and 

 probably includes an undifferentiated gular region. 



The ventral muscles have the customary origins and insertions. 

 The ventral adductors of the labium {2adlh) arise on the tentorium 

 {Tent) and insert on the base of the first prementum near the mid- 

 line. The sclerite of the first prementum has become extended slightly 

 posteriorly in the center to form a point of attachment for these 

 muscles. The retractors of the prementum {rst), a comparatively 

 large pair of muscles, arise on the postmentum and insert on the base 

 of the second prementum. 



Pyrochroidae (pi. 5, B). 



The customary division of the labium into the first prementum 

 and the second prementum, together with the postmentum, is shown 

 by this species. The labium is somewhat unusual in that it has a 

 considerably elongated ligula {Lig). The postmentum {Pmt) is sepa- 

 rated from the second prementum {IlPrmt) by a membranous area, 

 and extends posteriorly as far as the proximal ends of the posterior 

 tentorial pits {pt). The gula {Gu) is a separate sclerite lying posterior 

 to the tentorial pits and the postmentum. 



There are the usual muscles in this species. The retractors of the 

 prementum {rst) arise on the postmentum in line with the anterior 

 ends of the tentorial pits and insert on the base of the second pre- 

 mentum. The ventral adductors of the labium {2adlh) originate from 

 the posterior tentorium {Tent) and insert on the base of the first 

 prementum {IPrmt). 



Pythidae (pi. 5, D). 



In external appearance the labium of Pytho shows no unusual 

 features, although it does carry a prominent ligula {Lig). The first 

 prementum {IPrmt) carries the palpi and is set off from the second 

 prementum {IlPrmt) by a membrane. The postmentum {Pint) is 

 likewise separated from the latter subdivision by a membranous area. 



There are two pairs of ventral muscles to be found in the labium 

 of this species. The retractors of the prementum {rst) originate on 

 the postmentum and insert on the base of the second prementum. 



