stough: the hackberry psylla. 129 



triangular and extends forward about as far as the end of the 

 labrum and is called the maxillary sclerite (fig. 1, mxs). The 

 end of this sclerite has a rather slender, curved portion at its 

 apex, called the "maxillary process." These two sclerites are 

 shown in figure 3 in ventral aspect, and in figure 1 in lateral 

 aspect, where the clypeus, labrum, setse, etc., have been bent 

 ventrad in order to show the parts free and not overlapping. 

 The edge of the maxillary sclerite and maxillary process are 

 also shown in figure 5 looking ventrad. According to Smith 

 (1892) these two sclerites represent the true mandibles and 

 maxillae, the setse not being considered as such. 



Mouth Parts Proper. Labrum. — The labrum (29-S and 1, 

 lab) is only about half as long as the clypeus and differs in 

 shape from the labrum of the cicada in that instead of being a 

 narrow, pointed process, it is, as viewed from in front, rec- 

 tangular in general shape, slightly longer than broad, with 

 distal corners rounded. It is not so flat as in the cicada, but 

 its lateral edges are bent dorsad in the same manner as those of 

 the clypeus, so as to partly surround the setse and the pharyn- 

 geal canal. At the proximal end of the labrum is found a 

 slightly curved suture between it and the clypeus. This suture 

 was very hard to make out, and the two sclerites in some speci- 

 mens appeared almost as if fused. Viewed from one side, the 

 ventral outline of the labrum is seen to be slightly convex, with 

 the distal portion bent somewhat ventrad. Marlatt's nomen- 

 clature makes the frons the clypeus and the clypeus and la- 

 brum a two-piece labrum. 



Epipharynx. — Situated under the labrum (29-2, 3 and 1, 

 ep), and shorter than the same, is an indistinct organ, the 

 epipharynx. In the psyllid this organ is a delicate, fleshy, 

 tongue-like structure, more or less triangular in shape, with a 

 blunt tip, extending as a sort of outgrowth from, and exten- 

 sion of, the labrum. It appears as if it were a prolongation of 

 the labrum, and it was difficult in most cases to determine 

 where the one ended and the other began. The epipharynx is 

 pressed tightly upon the upper surfaces of the setse, surround- 

 ing them somewhat on the sides, and thus supplements the la- 

 brum in keeping them together to form a tube. 



Labium. — The labium is attached below the hypopharynx, on 

 the lower side of the head (29-1, labi, and 3^-6). This at- 

 tachment is by means of a delicate membrane made fast to the 



