Nov., 1920] Zygopterous Dragon Flies 23 



5. Polythorinae. Fi<;s. 1(5-27. Miocora, Cora, Eulhore, Polythore, 



Chalcopteryx. 



Miocora and Cora are the most generalized genera. This and 

 the preceding family form a short lateral branch at the base of 

 the Agrionid tree characterized by ventral gills in the naiad. ^^ 

 The peculiar arculus is not primitive but is derived from a 

 normal arculus as is shown by the position of its upper end in 

 the angle formed by M4. It has been pulled into this illogical 

 position by the shorteni?tg of the upper limb of the arculus. 



The ventral abdominal gills are considered by the writer to 

 be specialized and not archaic, i. e., they do not hark back of 

 the Zygoptera to Ephemerid gills or the like. The primitive 

 method of breathing in the Odonate orders seems to have been 

 rectal because that is the method in the Anisoptera and in the 

 ■first two instars in Zygopterous naiads. Also any Zygopterous 

 naiad lives normally by rectal breathing after the external gills 

 have been removed. If this is true the caudal gills are a com- 

 paratively late acquisition which applies also to the ventral 

 paired gills. The writer reasons that the slender stature of the 

 adult Zygopter was reflected in the larva or developed there 

 parallel, that with the diminishing diameter of the abdomen the 

 rectal gill basket became crowded which necessitated the 

 development of external gills. This development of external gills 

 then took place along two lines. 1. Caudal and ventral gills in 

 the Polythorine-Epallagine branch; and 2. Caudal gills in the 

 other Zygoptera. 



6. Agrioninse. Figs. 42-73. Caliphcea, Neocharis, (Dicterias), Helio- 



. charis, Cyanocharis, Phaon, Vestalis, Lais, Hetacrina, Mnais, 

 Psolodesmus, Climacobasis, Umma, Sapho, (Archineura), Agrion, 

 Matrona, Matronoides, Neurobasis. 



The first eight are the primitive forms, while Archineura, 

 Matronoides and Neurobasis are highly specialized in rich vena- 

 tion and naiadal characters. CaliphcBa shows relationship to the 

 EpallagincB in the recurrent penis lobes, but to the primitive 

 Agrionines, especially Hetcerina and the South American series 

 in its arculus and quadrangle. A study of the penes, figs. 48-53, 

 at once showed the South American series of Neocharis, Helio- 

 charis and Cyanocharis to be Agrionine. These are in South 

 America where primitive genera might be expected and again 



12 Calvert, Ent. News, XXII, pp. 49-64, 1911. (Cora). 



