340 STEPHEN G. RICH 



D. Subfamily Libellulinae 



The nymphs of this family are, as a whole, as much alike as 

 in the other two subfamilies, the agreement of the several species 

 of Libellula with conditions found in Plathemis is noticeable. 

 But a number of genera, including Pantala and Tramea (figs. 

 30 and 31), show a distribution of tracheal branches slightly 

 different from that found in Plathemis. The gills of Leucor- 

 hinia intacta have the form shown in figure 34. The tracheal 

 distribution to the gills in this species is shown in figure 23. 

 There are eighteen gills in each row and they are all alike in 

 size; their tracheation is marked by an unusually parallel ar- 

 rangement of tracheoles in the gill body. Sympetrum obtru- 

 sum (fig. 35) offers somewhat of a different form of gill. The 

 shape is here like a quarter of a circle, or perhaps more nearly a 

 quarter of an oval, with the straight edge caudal. The cushion 

 is unusually small. 



The rectums of Pantala flavescens and Tramea Carolina are 

 specialized in that the gills at the two ends of the rectum have 

 not the same size and shape. They agree in tracheation, and 

 show the extreme type of bunching of branches. I figure the 



Fig. 30 Dorsal view of rectum of Tramea Carolina. 



Fig. 31 Ventral view of rectum of Pantala flavescens. 



Fig. 32 Typical gill of Dorocordulia libera. 



Fig. 33 Caudalmost gill of same. 



Fig. 34 Gill of Leucorhinia intacta. 



Fig. 35 Gill of Sympetrum obtrusum. 



Fig. 36 Gill of Tramea Carolina. 



Fig. 37 Gradation in size of gills of same; largest gills are at caudal end of 

 rectum. 



Fig. 38 Gill from cephalic end of rectum of Pantala flavescens. 



Fig. 39 Gill from middle of rectum of same. 



Fig. 40 Gill from caudal end of rectum of same. 



Fig. 41 Setules from tip of gill of same. 



Fig. 42 Dorsal view of rectum and small intestine of Argia putrida. 



Fig. 43 Ventral view of intestinal ampulla of same. 



Fig. 44 Dorsal view of anal valve of Plathemis lydia, with superior append- 

 age cut away, a single lobe is also shown separately. 



Fig. 45 Caudal aspect of anal valve of Basiaeschna janata. 



Fig. 46 Dorsal aspect of rectum of Lanthus parvulus. 



Fig. 47 Ventral aspect of same. 



Fig. 48 Longitudinal and buttress folds of same. 



