156 PHILIP p. CALVERT. 



The preceding descriptiou of the parts of the epicranium applies 

 to the Agrionidse and the Gomphinse, except that in the latter the 

 occiput is se[)arated by distinct sutures in front and on either side, 

 but behind it fuses with the epicranium. In the remaining groups, 

 where the eyes meet in a greater or less extent on the top of the 

 head, the area of the epicranium is much reduced. Little remains 

 of the vertex, except that part included between the ocelli, which is 

 elevated and often characteristically shaped in different genera ; it 

 is the frontal vesicle of some authors. The gen^e are almost entirely 

 obliterated. The frons is bent on itself at an obtuse angle so that 

 two surfaces may be distinguished, one horizontal (superior surface), 

 the other more or less vertical (anterior surface). Behind the eyes 

 the epicranium continues to occupy a considerable area. 



The ocelli are three in number, placed upon the vertex in the form 

 of an isosceles triangle with its apex directed forwards. The ante- 

 rior ocellus is the largest of the three. 



The occipui is situated at the upper, median, posterior portion of 

 the head from the vertex backwards and downwards to a short dis- 

 tance above the posterior foramen, which latter it does not reach. 

 As already mentioned, it is entirely fused with the epicranium in 

 the Zygoptera, but is more or less distinct in the Anisoj)tera. It 

 presents two more or less distinct surfaces, one dorsal, the other pos- 

 terior ; where these are sharply separated, as in the Gomphinai, the 

 separating margin (referred to as " hind margin," or simply "mar- 

 gin") frequently offers specific characters. 



The <jida is membranous and extends from the posterior foramen 

 to the submentum. 



The clypeus (ejnstoma) is wider than high. A division into ante- 

 {ivjra-) and ^90.s^ (supra-) clyjieus exists, the former having received 

 the special name of rhiriarimn, the latter that of nasus ; they form 

 an obtuse angle with each other in the Zygoptera, but lie more nearly 

 in the same plane in the Anisoptera. 



The lahrum is of moderate size, elongated horizontally, its basal 

 margin nearly straight, its free edge rounded. 



The antennoi are quite short, bristle-like, and are inserted on the 

 epicranium between frons and vertex. Each consists of at least four 

 joints, of which the basal is usually thickest and shortest. The re- 

 maining joints successively decrease in thickness, their comparative 

 length varies in different genera. 



