NO. 3 



INSECT IIEAl 



-SNODCKASS 



97 



B, C, ER), from the lateral parts of which arise the anterior tentorial 

 arms {AT). The roots of these arms appear externally as lateral 

 slits in the epistomal sutm-e (figs. 36 B, 37 A, at, at), just mesad 

 to the anterior articulations of the mandibles {c, c). The clypeus of 

 Dissostcira is partially divided by transverse lateral grooves into 

 anteclypeal and postclypeal areas. The labrum is a 1)road oval plate, 

 notched at the middle of its ventral margin, freely movable on the 

 lower edge of the clypeus. A median quadrate area on its basal half 

 is limited below by a sinuous transverse groove (fig. 37 A) that forms 

 a low ridge on the inner surface of the anterior wall (B, /.) On the 



AT 



Clp— 



-Lm— 



Tor 



A 



B 



Fig. 2)7- — Clypeus and labrum of Dissostcira Carolina. 



A, anterior surface. B, posterior surface of anterior wall, showing muscle 

 attachments, and bases of anterior tentorial arms. 



AT, anterior arm of tentorium; at, anterior tentorial pit; c", anterior articula- 

 tion of mandible ; Clp, clypeus ; es, epistomal suture ; /, ridge of anterior labral 

 wall; Lm, labrum; Tor, torma ; /. labral compressors; ^, anterior retractors of 

 labrum; 3, posterior retractors of labrum; 34, 35, points of origin of anterior 

 dilators of buccal cavity (figs. 41, 44). 



posterior surface of the clypeo-labral lobe, the area of the clypeus is 

 separated from that of the labrum by two small chitinous bars, the 

 tonme (figs. 37 B, 42 A, Tor). A median Y-shaped thickening (fig. 

 42 A, 7/0 of the cuticula of the labrum makes a ridge on the inner 

 surface of the posterior labral wall. 



The clypeus has no muscles for its own movement, but the first 

 two pairs of anterior dilators of the buccal cavity (figs. 41, 44, 33^ Si) 

 are inserted on the inner surface of its anterior wall (fig. 37 B, jj, 

 34) . The labrum is provided with three sets of muscles, as follows : 



I.— Compressors of the labrum (fig. 37 B).— A pair of short mus- 

 cles arising medially on transverse ridge of anterior labral wall (/) ; 

 diverging to arms of Y-shaped ridge in posterior wall (fig. 42 A. m). 



