200 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 43. 



4. The function of Dromogomphus is that of a filler-in or supple- 

 nienter. Along the quiet reaches of the river it completes the work 

 of the Macromias, at the ripples that of the two species of Gomphus, 

 and everywhere it makes good the deficiencies and omissions of these 

 other dragon fhes. Although often far more numerous than the 

 Macromias, its inferior size and agility compel it to be satisfied wdth 

 second place. And at the ripples, while it could hold its own with 

 either species of GompTius on equal terms, it is always greatly out- 

 numbered. 



5. Among the damsel flies the two species of Hetxrina occupy the 

 same position as the Macro mias among the dragon flies. Wliile they 

 are found in greater numbers near swift water, they nevertheless 

 cover practically the entire river. But there is this difference, that the 

 species are separated, americana occupjdng the upper portions of the 

 river among the mountains, while tricolor is found in the lowlands 

 farther down. The species, therefore, can not be counted as two in 

 comparison with those of Macromia, but only as one. 



6. Four of the species of Argia, namely, moesta putrida, apicalis 

 tibialis, and translata, correspond very well with the two species of 

 Gomjjlius. 



While they are not confined to the vicinity of swift water, like those 

 dragon flies, they do congregate in considerable numbers at favorable 

 localities. 



7. The odonate fauna of the Cumberland Elver is thus made up 

 practically of these five dragon fhes and six damsel flies, and all the 

 other species here enumerated are in a measure mcidental or acces- 

 sory. 



8. The general course of the Cumberland River is a crescentic 

 curve, convex toward the south, so that the mouth is practically on 

 the same parallel as the source. Nevertheless the combination of 

 mountains, an elevated plateau, and lowlands results in a correspond- 

 ing combination of northern, cosmopolitan, and southern species in 

 the odonate fauna. 



