4 PROCEEDIT^GS OF THE NATIONAL MUSEUM. vol. 64. 



Prothonix with a sharp lateral, dorsal lobe and a large anterior, 

 supracoxal process. (See fig. 12.) Wing pads reaching to segments 



5 and 6 of the abdomen. Legs straight and slender with the tibia 

 hairy and armed with two well-developed rows of long slender 

 spines — a tibial armature remarkably like that of a Zygopterid 

 imago. Tarsal claws simple. 



Abdomen elliptical, widest at about segTaent 6, tapering regularly 

 to segment 2 in front and to segment 9 behind. Segment 10 a nar- 

 row ring inserted into the posterior concavity of segment 9. (See figs. 

 9 and 10.) Large dorsal hooks on segments 7-9. A mere suggestion 

 of a tubercle on segment 6, which was not visible until the incrust- 

 ing mud had been scraped away. Segments 8 and 9 with lateral 

 hooks, which are small on 8 but on 9 are longer than half the length 

 of the segment. The lateral hooks slightlj^ incurved and reaching 

 nearly to the apex of the abdominal appendages. Segment 10 a ring 

 whose dorsal length is about one-third of that of segment 9. Middle 

 appendage broadly conical and more than three times as long as 

 segment 10. Superior appendages subequal to the middle append- 

 age, their apices acute and decurved. Inferior appendages slightly 

 longer than the others, their apices acute but less decurved than 

 those of the superiors. 



EXPLANATION OF THE PLATE. 



The drawings are by the author. 



Figs. 1-5. Helocordulia uJUeri. 1, mature naiad ; 2, mentum and lateral lobe 

 of labium ; 3, lateral lobe of labium ; 4, dorsal aspect of ab- 

 dominal segments 7-10 ; 5, lateral aspect of abdominal segments 

 7-10. 

 6-12. Helocordulia selysii. 6, naiad; 7, labium; 8, labial lobe; 9 and 10, 

 segments 7-10 of abdomen; 11, antenna; 12, prothorax. 



