304 The Ohio Journal of Science [Vol. XVI, No. 7, 



the case of the Bythoscopidae they have been carried over 

 and down on the face, while the dorsal surface of the vertex 

 is greatly reduced. 



The Front, although a true sclerite, is not readily differ- 

 entiated from the following sclerite — the clypeus (clyp.) — the 

 suture between them being obsolete, but its position can be 

 judged by the fact that the anterior arms (i. a.) of the tentorium 

 are invaginated on each side, where the suture should normally 

 end. The front usually, at least in the more generalized insects, 

 can be identified owing to the fact that it bears the median 

 ocellus, but no trace of such an ocellus is to be found in the 

 Jassid head. The frontal region ("frontal ridge") then would 

 be the area between the cephalic margin of the head and a 

 transverse line connecting the invaginations of the anterior 

 arms of the tentorium. In the Jassoid head these invaginations 

 occur at the cephalic end of the maxillary suture, on the so-called 

 mandibular plates or lorae. Its lateral margins would be 

 defined by the longitudinal sutures on either side of the head. 



The clypeus (clyp.) is the sclerite attached to the frons 

 along its anterior margin. In the Jassid head as in other 

 Homoptera, it is not easily distinguished from the front; it 

 is a broadly rectangular sclerite, generally somewhat convex 

 with its lateral margins developed into two plates (lorae) which 

 attach along the sides of the labrum. These two plates (the 

 lorae or so-called mandibular plates) have long been regarded 

 as the external pieces of the mandible, although in reality they 

 have no connection with the mandibles. Muir and Kershaw 

 have shown conclusively in their work on the development of 

 the mouthparts of the Homoptera, that the mandibles become 

 enclosed within the head in the course of development. No 

 true suture exists where these two plates are in relation to the 

 labrum, but their basal portion is attached strongly to the middle 

 piece of the clypeus. If we consider the mesal piece as the clypeus 

 proper, then the lateral developments might be regarded as 

 the antecoxal pieces of the mandible. 



The labrum (labr.) is the upper lip and is attached to the 

 anterior margin of the clypeus. It constitutes the roof of 

 the mouth and is differentiated with difficulty from the clypeus. 

 However the anterior margin of the clypeus is connected with the 

 pharynx by two small developments of the tentorium, and these 



