MEEK : MOUTH-PARTS OF THE HEMIPTERA. 261 



EXTERNAL AREAS OF THE HEAD. 



The general appearance of the Cicada head is familiar to 

 most students. It is an isosceles triangle in shape. The vertex 

 of the head marks the base, and at the basal angles are the 

 large compound eyes. From the lower angle extends the 

 slender, three-jointed beak or proboscis. From the cephalic 

 aspect, the most prominent part of the head is the swollen, 

 deeply furrowed frons. Beneath it is the smaller, roof-like cly- 

 peus. Laterad of both frons and clypeus lie the crescent-shaped 

 lorae or mandibular sclerites. Still laterad of these lie the 

 narrow maxillary sclerites. From the vertex to the tip of the 

 beak the head averages 10 mm. in length, and from eye to eye 

 it averages 7.5 mm. 



The Epicranium. — (Fig. 1, e.) In generalized insects the 

 dorsal surface of the head is marked by a well-defined Y-shaped 

 epicranial suture. The sclerites lying back of the arms of the 

 letter and adjoining the stem form an area known as the epi- 

 cranium. Such aa area (fig. 1, e) is easily observed in the 

 Cicada, but the suture is T-shaped. The cephalic part of the 

 epicranium is called the vertex, and this bears the three ocelli. 



The Frons. — (Fig. 1, /. ) Between the epicranial suture 

 and the beak are three sclerites. The first of these and also the 

 largest, a convex shield in shape, occupies the middle part of 

 the cephalic aspect of the head, and is named the frons. The 

 sclerite is protruding, with a deep wrinkle or fold along the 

 median line. On each side, running laterad, are series of 

 furrows, usually eight in number. The lower edge of the 

 frons is narrower than the upper, and the junction with the 

 clypeus is made in a curved line. 



The Clypeus. (Fig. 1, c.) The clypeus is the intermediate 

 of the three cephalic sclerites. It resembles the frons in shape, 

 but is considerably smaller in size. The elevation along the 

 median line continues as in the sclerite above. The deep me- 

 dian sulcus, however, which is so characteristic of the frons, is 

 not present. 



The Mandibular Sclerites. (Fig. 1, md.s.) These have 

 already been mentioned as lying laterad of both the frons and 

 clypeus. They are crescent-shaped, sparsely covered with long 

 hair, and are closely applied to the sides of the head. Dorsad 



