304 W. D. FUNKHOUSER 



The vertex likewise consists of two sclcritcs, separated by the epicranial 

 suture, and makes up the largest area of the cephalic part of the head. 

 The sclerites are equal in^ size and are complements of each other in shape 

 and position. The vertex occupies all that part of the head between the 

 compound eyes, and between the occiput above and the clypeus and genae 

 below. In each sclerite is located an ocellus. As has been noted, the 

 relative position of the ocelli in the vertex is vanable, the migrations of 

 these organs being both sidewise and up and down. They are always, 

 however, in a line with each other horizontally, and equidistant from the 

 epicranial suture. In shape each sclerite of the vertex is roughly 

 pentagonal, the basal, or dorsal, part often being sinuate to follow the 

 anterior margin of the prothorax into which it fits snugly. On the whole 

 the vertex shows considerable variation in form, and the lower cephalic 

 edge is often infolded to form a sharp angle over the base of the antennae. 



The clypeus is one of the most variable, most prominent, most interest- 

 ing, and most important of the sclerites of the head. The position of 

 this sclerite with reference to the vertex is, however, constant and no 

 difficulty is experienced in locating it. The position of the clypeus as 

 an unpaired sclerite between the arms of the epicranial suture suggests 

 at once the possibility of confusing it with the frons. This indeed would 

 be the natural conclusion, did not the location of the sclerite with reference 

 to the arms of the tentorium of the endoskeleton preclude such a possi- 

 bility. The anterior arms of the tentorium have been shown (Comstock 

 and Kochi, 1902:39-42) to arise as invaginations at the cephalo-lateral 

 angle of the clypeus or between the clypeus and the frons. In the case 

 of the Membracidae these arms undoubtedly reach the cephalic margin of 

 the sclerite in question, altho they have migrated slightly to the laterad. 

 It would be impossible, therefore, to reconcile the conclusion that this 

 sclerite represents the frons, with any of the previous work done on the 

 subject, and it seems evident that it must be considered as the clypeus. 

 In fact such a conclusion accords perfectly with the work done by Bentley 

 (1900) on the cicada, in which he shows that the large projecting sclerite 

 commonly known as the frons in that insect is in reality the clypeus. 



In shape the clypeus is generally subquadrangular as seen from before, 

 but projects backward at its extremity to form a deep, rounded keel 

 (Plate XXXI, 2). This keel articulates with the gena on either sidci, and 

 lifts the distal end of the clypeus up from the anterior outline of the head 



