716 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXVI. 



obtruding- ang-le of the cubitus, and are of tenest confluent through the 

 atrophy of the middle cross vein. To the four-sided figure, which 

 together they always present, we will apply the technical term 'N(uad- 

 rangle" {</, of all the figures; also called elsewhere "quadrilateral, aud 



Fig. 9. — Wings OF a fossil, i'NnEscRiBi:i), Ageionik genus, in thk Museum ofCompar.^tive Zoology. 



quadrangular space"). The fossil Agrionid genus illustrated in fig. 9 

 oflers easy transition from the conditions just seen in the Anisoptera 

 to those of the Zygoptera, and renders homologies plain. Com- 

 paring this wing with the fore wing of T(irathemi>< (fig. 10) with respect 



Fig. 10.— Win(js of Tdnitlmnisf liiialina Kikhy. 



to the points in question, triangle and supertriangle are recognizable 

 readily in both (though in Tefrathemls the latter is elongated and con- 

 tains an extra cross vein), and both may easily be derived from ordinary 

 rectangular cells. 



