536 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



again as the ninth, and a little more than half as long as the seventh. 

 The anal appendages were rounded triangular, as long as the tenth 

 segment. 



Dysagrion fredericii. — Several specimens of various parts of the body 

 with wings were found by Mr. F. 0. Bowditch (after whom the species is 

 named) and myself in the Green River shales, in a railway cutting by 

 the river bank beyond Green River Station. The most important are a 

 nearly perfect wing and its reverse (Nos. 4167, 4168), which preserve 

 all the important points of the neuration. A single antechbital appears 

 to be present, nearer the nodus than the arculus ; the principal sector, 

 like the short sector {sector brevis), bends slightly upward just as it 

 reaches the arculus j the cellules in the discoidal area are half as broad 

 again as long, yet the breadth of the wing is such that the broadest 

 part of the postcostal space, between the nodus and the middle of the 

 wing, is more than half as broad as the rest of the wing at that point. 

 The wing is wholly hyaline, excepting the infumated pterostigma, 

 which is bordered by thickened black veins, and surmounts four cellules 

 at its lower margin ; the veins of the wing generally are testaceous ; 

 there are 20 postcubitals. 



Probable length of the wing 38-39^1""; length of part beyond 

 peduncle 34™™, breadth 9™™ ; distance from nodus to tip of wing 

 23™™ ; length of pterostigma 3.5™™. 



Another wing from the same beds with its reverse (Kos. 4165, 4166) 

 is very fragmentary, showing little besides the border of the apical 

 half of the wing with the pterostigma, and most of the postcubital 

 uervules. I have here considered it the hind wing of the same species, 

 from its similar size, the exact resemblance of the pterostigma, which 

 also surmounts four cellules, and the indication of a similar profusion 

 of intercalated supplementary nervules. It seems, however, not im- 

 probable that it may prove to be a second species of the same genus, 

 from the great difference in form. The two borders of the outer half of 

 the wing are nearly parallel, and the apex falls a little below the mid- 

 dle. This difference, however, really concerns only the posterior curve 

 of the wing below the apex. The nodus is not preserved. Greatest 

 breadth 7.5™™. 



Considering the fragments of heads, etc., referred to under the genus 

 as belonging to this species, we have to add Nos. 4179, 4180, and 4183 

 (besides No. 62 of Mr. Richardson's collection) as representing heads ; 

 Nos. 4183, 4184, the united head, thorax, and base of wings ; and Nos. 

 4170, 4173, 4174, 4177, 4178, as parts of the abdomen. The abdomen 

 shows a slender, dorsal, pale stripe, distinct and moderately broad on the 

 sixth to the eighth segments, scarcely reaching either border, and 

 posteriorly expanding into a small, round spot; and a faint dorsal line 

 on the fourth and fifth segments, interrupted just before the tip. The 

 appendages are simple. 



Length of head (according to the mode of preservation) 4.0-4.5™™j. 



