56 Annals Entomological Society of America [Vol." XV, 



fused. Sinistral lobe with a dorsal plate and two copulatory 

 processes or titillators, of which the ventral represents the 

 paramere (?), and one or two accessory processes; dextral lobe 

 with a dorsal plate and a small ventral clasper. 



IsoPTERA. Terminal segments scarcely abbreviated; the 

 tenth tergum prolonged, serving as a supra-anal plate; ninth 

 sternum forming a large undivided hypandrium, bearing styli; 

 cerci short, of two to several segments; true supra-anal plate 

 absent as a distinct structure; paraprocts broad and somewhat 

 flattened, but little chitinized ; penis absent or reduced to a small 

 membranous lobe, the genital aperture single and median; no 

 copulatory processes present. 



ZoRAPTERA. Ninth tergum abbreviated; tenth fused with 

 supra-anal plate and paraprocts; cerci short and unsegmented; 

 ninth sternum absent or membranous, the eighth apparently 

 taking its place as a hypandrium; penis consisting chiefly of 

 two asymmetrical processes, the sinistral a slender titillator, 

 the dextral a large lobe bearing a subapical dorsal hook; position 

 of genital aperture unknown. 



Odonata. Terminal segments elongated, the genitalia 

 ventral in position ; ninth sternum consisting of sternite and two 

 separate, rudimentary coxites, without styli; the membrane 

 between the ninth and tenth sterna somewhat chitinized so as 

 to appear to belong to the ninth sternum; tenth sternum 

 distinct ; true or primitive penis very small and simple, without 

 parameres (replaced by secondary penis on sternum of segment 

 2) ; cerci short and unsegmented ; supra-anal plate elongate 

 and projecting (Anisoptera) or small and inconspicuous, 

 (Zygoptera) ; paraprocts rather large, without appendages 

 (Anisoptera), or with copulatory processes (Zygoptera). In 

 nymphs of many genera indications of a possible twelfth segment 

 are present. 



