Dokring: Lepyronia quadrangularis. 541 



that the vertex and the front lie entirely on the dorsal surface and 

 the remaining sclerites on the ventral surface. Thus the anterior 

 margins of the front and vertex (pi. T.V, fig. 1) have been pressed 

 against the anterior margin of the clypcus, which together form 

 the cephalic and lateral margins of the head. The head, as is shown 

 in the figure, projects straight forward on a line with the body and 

 the beak projects backward and lies between the coxse when at rest. 



In the literature the most commonly accepted homology of the 

 sclerites of the head are as follows: On the ventral aspect the large 

 protruding sclerite (pi. LVI, fig. 2) is called the front; the smaller 

 sclerite attached to its posterior margin, the clypeus; and the 

 smaller triangular sclerite fastened to the clypeus, the labrum. The 

 entire dorsal portion of the head (pi. LVI, fig. 1) is usually desig- 

 nated as the vertex, although it consists of two sclerites. The larger 

 of these occupies most of the entire surface with the exception of the 

 broad invagination in the cephalomedial region, into which a small 

 subrectangular sclerite, the tylus, is inserted. There seems to have 

 been no attempt to homologize or account for the existence of the 

 tylus, although it appears as a definite sclerite in the adult and is 

 partially indicated in the later nymphal stages. 



Partly because of the lack of explanation with regard to the tylus 

 and partly because of the suggestion of other workers in other 

 groups, an investigation with regard to a different homology of 

 parts was attempted. Funkhouser (1917) states that the clypeus in 

 the Membra cidae is determined by the location of the anterior 

 arms of the tentorium, which fully accords with the view of Com- 

 stock and Kochi (1902), that the anterior arms of the tentorium 

 arise as invaginations of the body wall between the clypeus and 

 front. He also refers to Bentley's work (1900) on the Cicada, which 

 was unjuiblished, wherein the latter shows that the large, protruding 

 sclerite known as the frons is really the clypeus. Several other 

 articles in support of this theory have been found. Marlatt 

 (1896) calls the sclerite in question (pi. LVI, fig. 2) the clypeus; 

 likewise Smith (1892). Bugnion and Popoff (1911) state:" "One 

 of the characteristics of the clypeus is that it serves for insertion, 

 with its deep face, of the anterior bundles of the dilator of the 

 pharj^nx. A clypeus cleared in balsam shows in all Hemiptera the 

 linear insertion of the striated membrane (of the pharynx) and the 

 two sides of transverse lines which correspond to the insertion of 

 nauscles. Among some species (Cicada) the transverse lines are 

 indeed seen from the exterior and give a particular appearance to 



