132 TERTIAEY INSECTS OF NORTH AMERICA. 



2. DYSAGRION LAKESII. 



A nearly perfect wing and its reverse represent another species of this 

 genus, which is more nearly allied to D. packardii than to 1). fredericii, 

 differing from the former principally in the form of the quadrilateral and 

 the shape of the pterostigma, which, although as. long as there, surmounts 

 only three cellules. There are two antecubitals, one at, the other a little 

 before, the arculus ; the base of the principal and short sectors is straight, 

 the cellules in the discoidal area are much as in D. fredericii, the quadri- 

 lateral is twice as long as its mean breadth, its basal margin half as long- 

 as its apical, and the vein forming the lower margin bent at a similar angle 

 with the inferior vein of the triangle as in D. fredericii; the nodus is placed 

 at one-third the distance from the arculus to the pterostigma. The wing is 

 hyaline, excepting the fuliginous pterostigma, which is four times as long 

 as broad, surmounts three cellules, and is bordered by thickened black veins; 

 its outer margin is much more oblique than its inner ; there are nineteen 

 .postcubitals. 



Probable length of wing, 35 mm ; length of part beyond peduncle, 

 33 mm ; breadth, 8 mm ; distance from arculus to nodus, 8 mm ; from nodus to 

 tip of wing, 22.5 mm ; from nodus to inner corner of pterostigma, 15.5 mm ; 

 length of pterostigma, 3.75 mm . 



Named for Prof. Arthur Lakes, of Colorado, my companion in explor- 

 ing the fossil insect beds of the West. 



Green River. One specimen, Dr. A. S. Packard, Nos. 259 and 260. 



3. DYSAGRION PACKARDII. 



PI. 6, Figs. 1, 3, 11. 

 Dysagrion packardii Scudd., Zittel, Handb. d. Palaeont., I, ii, 776, Fig. 979 (1885). 



Another species of this genus is represented by a nearly complete 

 front wing, a fragment of a wing and its reverse, and by a tolerably per- 

 fect body presumably belonging to it. The wing agrees with that of D. 

 fredericii in form and size, but differs in the following particulars: No ante- 

 cubitals exist, except in the neighborhood of the arculus, one being present 

 nearly half-way from it to the base and another may exist in the broken 

 part of the wing just beyond the arculus ; the base of the principal and 

 short sectors is straight ; the cellules in the discoidal area are, if anything, 



