124 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8[ 



has taken place in the Hymenoptera. In the larval head of Vespa 

 (fig. 46 D) the clypeus has clearly encroached upon the area of the 

 frons by a dorsal arching of the epistomal suture {cs). In an adult 

 tenthredinid (E), the same condition is observed, but the lower parts 

 of the frontal sutures {fs) are lost, and the bases of the antennae 

 have approached each other mesally, and have constricted the frontal 

 area between them. In the adult of Apis (F) the condition is more 

 exaggerated — the epistomal suture {es), identified by the tentorial 

 pits {at, at), is arched upward almost to the bases of the antennae, 

 and the frontal sutures are obsolete. The frontal area (Fr), however, 

 is to be identified by the position of the median ocellus, and the points 

 of origin of the labral muscles between and just aljove the antennal 

 bases. The head of a larval tenthredinid (fig. 46 C) presents a 

 specialized condition, for the single large facial plate is here clearly 

 a fronto-clypeus, as shown by the origin of the labral muscles on 

 its upper parts, and by the origin of the tentorial arms {AT) from 

 the ridges at its sides. Evidently, the median part of the epistomal 

 ridge and its suture has been suppressed. A similar condition is to 

 be observed in some trichopteran larvae. 



A still greater degree in the upward extension of the clypeus is 

 shown on the face of a psocid (fig. 46 G). Here the epistomal suture 

 {es) is arched high above the tentorial pits {at, at), and the clypeus 

 {Clp) becomes the large, prominent, shield-shaped plate of the face 

 between the bases of the antennae. The frontal sutures are lacking, 

 but the frontal area (Fr) is that between the bifid end of the coronal 

 suture and the clypeus, on which is located the median ocellus. A 

 weakly chitinized area below the clypeus is sometimes called the 

 anteclypeus {Aclp), but it appears to be only a chitinization of the 

 connecting membrane between the clypeus and the labrum. 



The clypeus, finally, attains its greatest development at the expense 

 of the frons in the Homoptera (fig. 47 D). In the cicada (fig. 46 H), 

 the clypeus is the great bulging, striated plate of the face upon which 

 arise the dilator muscles of the mouth pump. The dorsal arch of the 

 epistomal suture {cs) lies on a level with the antennal bases, and the 

 anterior tentorial pits {at, at) are in its upper lateral parts, just above 

 the dorsal extremities {c, c) of the mandibular plates (Md). The 

 frons is a small, indistinctly defined triangular area {Fr) bearing 

 the median ocellus in the adult. It is more strongly marked in the 

 nymph, and is cut out by the opening of the frontal sutures at the 

 time of the molt. The plate below the principal clypeal sclerite is 

 probably an anteclypeus {Aclp), because in some Hemiptera it is not 

 distinctly separated from the area above it, but it is questionable if 



