1911] Muir and Kershaw — Alouth-parls of Hemiptera 3 



forms it is hard to homologize them with mandibles without 

 some knowledge of the more generalized forms. 



The Cercopid head (Fig. 2) is similar to the Cicada. The 

 clypeus (clr) is large; the mandibular sutures (ms) run half way 

 along its sides; the frontal ridges (//•) are drawn out over the 

 antennae, and along the basal sides of the clypeus, and the gula 

 is greatly reduced. The mouth parts of the Tetigonids are easily 

 homologized with these. 



In the Membracids (Fig. 3) all the same parts can be plainly 

 seen. The clypeus {clr) is reduced somewhat basally; the mandi- 

 bular sutures (ms) approach nearer to the antennae; the frontal 

 ridges (/r) are well developed, and the gula is greatly reduced. 



Among the Derbids (Fig. 4) and Siphantas (Fig. 5) the head is 

 drawn out anteriorly; the clypeus (cl r) has its lateral parts (c) 

 long and the mandibular sutures (ms) running back to near the 

 base of the clypeus. In some species the eyes are comparatively 

 small and the genee large (Fig. 5, ge), in others the eyes are large 

 and the gense much reduced (Fig. 4, ge). The frontal ridges are 

 very little developed in these families. 



It is easy to homologize the head parts of most other families 

 of Homoptera with the families quoted above, but the Heteroptera 

 are more difficult. This is greatly on account of the gular region 

 being much more largely developed, thus preventing the deflec- 

 tion of the head and throwing the whole of the ventral and lateral 

 parts of the head forward. The frontal ridges are greatly devel- 

 oped, and alter the shape of the head, but this is also the case 

 among the Psyllids. 



Among the Lygseids (Fig. 6) the homologies of the head are 

 clear. The clypeus (cl r) with its lateral pieces (c) are well devel- 

 oped; the mandibular sutures (ms) run to near the antennae; the 

 maxillary plates (mxp), owing to the development of the gula 

 and the anterior position of the labium, are greatly shortened. 

 The frontal ridges are absent, unless the raised rim around the 

 antennae represents them. 



Among the Pentatomids the frontal ridges play a conspicuous 

 part. In Cyrtocoris they are large, project forward, and divari- 

 cate like horns. In Tessaratoma (Fig. 7) they are flatfish, project 

 forward, and meet along the central line (c. fr), the clypeus being 

 deflexed near its base, and passes between them (c. clr) The 



