470 CALIFORNIA ACADEMY OF SCIENCES. 



Hairs of the tibia^ about twice as long as the intervals between tliem; a 

 single row of postcostal cells; arculus complete, lying in the pro- 

 longation of the second antecubital; tarsal nails toothed, tooth 

 shorter than the nail proper. ArgUi. 



Hairs of the tibiae never twice as long as, but generally shorter than, 

 the intervals between them; otherwise as in Argia. 



$ with no apical ventral spine on 8. Postcostal vein separating 

 from the hind margin of the wing — in the majority of individ- 

 uals — at the basal i^ostcostal cross-vein or at a less distance in 

 front than the latter is long;* no pale postocnlar spots; abdomen 

 moderate; color red; tooth of tarsal nails very small. 



Erufhrag7-io7i. 

 $ with an apical ventral spine on 8.t Postcostal vein separating 

 from hind margin of wing at least as far in front of the basal 

 postcostal cross-vein as the latter is long; pale postociilar spots 

 present. 



Pterostigma of S similar in color on front and hind wings, no 

 dorsal bifid process on 10 (except E. exsulans 3 ). 



Enallagma. 

 Pterostigma of $ darker on front wings than on hind wings, 

 10 with a dorsal process, bifid at apex, in the males. 



Ischnura. 

 Subfamily Gomphin^. 

 Legion Gomphoides Selys. All or some of the triangles with cross-veins; 

 membraniile wanting or very small. 



Feet moderate (hind femora reaching back to 1); front wings with 



■upper side of triangle longer than the inner, outer side longest, 



broken, no supratriangulars, sectors of arculus separated at origin; 



frons prominent. Progomphus. 



Legion Gomphus Selys. All the triangles and the supratriangnlar sjiaces 



free; membranule wanting or very small. 



Superior appendages of S about as long as 10, each one bifid; inferior 

 appendage bifid, each branch bifid. No lateral membranous appen- 

 dages to 8. Vertex of ? tuberculous. Octogomphus. 



Subfamily ^Eschnin^. 

 I. Upper piece of arculus equal to or longer than the lower piece, its 

 upper sector arising a short distance above the lower sector, being sep- 

 arated from the latter by a distance h-l of that sei^arating the upjjer 

 sector from the median nerve. Supplementary sector between subnodal 



*' See the statistics on this subject given under Enjthragrion salmim, jwst. 

 t Except in Ischnura? erraiica n. sp. 



