122 HORTENSE BUTLER. 



The end hook is well developed, and of the outer lobe there is only 

 occasionally a trace. Ophiogomphus carolus PI. VII, Fig 5) shows 

 these characteristics as well as any species. A profusion of hairs 

 covers the entire labium, nientum, lateral lobes and all. In Gom- 

 phus vulgatissima (PI. VII, Fig. 5 a) the movable hook is long and 

 pointed, and the end hook also is of unusual length. The upper 

 lobe is a mere protuberance on the border of the lateral lobe. The 

 greatest development attained by the movable hook, however, is 

 shown in Aphylla edentata (PI. VII, Fig. 5 6), in which the mova- 

 ble hook is wonderfully long and slim, while the end hook almost 

 equals it. The upper lobe has entirely disappeared. 



Cordulegaster and Tachopteryx. 



Cordalegaster maculatus and TacJiopteryx thoreyi are the sole rep- 

 resentatives of their respective subfamilies, which I have studied. 

 Cordalegaster (PI. VII, Fig. 1) shows a mentum cleft to about one- 

 fourth its length. The cleft is wide and V shaped, and on either 

 point a small tooth is developed. The surface and border of the 

 mentum are covered with hairs. The lateral lobe is also thickly 

 covered with hairs, the movable hook is short and blunt, while the 

 end hook is long and sharp, and has a series of four small hooks 

 developed along its inner edge (PI. VII, Fig. 1 a). It will be shown 

 further on that the end hook of Calopteryx angustipemiis (PI. VII, 

 Fig. 6 e) exhibits one hook on its inner margin. These hooks, it 

 seems to me, may not improbably be considered a development carried 

 over from the nymphal condition. 



Tachopteryx thoreyi (PI. VII, Fig. 2) shows a ligula very similar 

 to that of Cordulegader. The mentum as well as the lateral lobe is 

 thickly covered with hairs. The movable hook is large but l)Iunt. 

 and the end hook is short, slender and incurved. 



ZYGOPTERA. 



In the Agrionidje the proportion of the width of the combined 

 ligula and mentum to its length is as 1 : 1, and the cleft in the 

 middle is always [jresent. It varies in depth from .75 to .20 of the 

 entire length and is proportionately wide. The existence of a suture 

 across the ligula has already been mentioned, and this suture as well 

 as the external border of the ligula is covered with hairs. The 

 movable hook is usually blunt, the end hook is very often larger 

 than the movable hook, while the outer lobe is not aj)parent. Both 



