232 PROCEEDINGS OF THE ACADEMY OF [May, 



12. Between Rs and Ms is one row of cells increasing to two rows. 

 156. Between Ms and M4 at the wing-margin are only three rows 



of cells, 

 17. Between M4 and Cm are (a) about three antenodal cells and 



(h) at the margin one row of cells. 



19. Between Cm and Cu2 at the wing-margin appear to be but one 



row of cells. 



20. Area posterior to Cu2 with no more than two rows of cells. 



21. Anal vein separating from the hind wing-margin (a) distad 



(fig. 12) or proximad (fig. 14) to the level of the arculus and 

 (6) at the level of the cubito-anal cross-vein (fig. 14, cross-vein 

 not shown in fig. 12). i"' 



22. No anal cross-veins, according to both figures. 



Comparison of the fossil Lithagrion (hyalinum) with 

 Phenacolestes. 



According to the figure and description of this ^Miocene genus 

 from Florissant, Colo., given by Scudder^^ and some notes on 

 more recently found specimens kindly communicated by Prof. 

 Cockerell, Lithagrion and Phenacolestes agree in the characters above 

 numbered 1, 3, 5, 7, 8, 9, 10 (probably), 11, 14, 15a, 16a and h, 18, 

 and differ in the following characters, the differences shown by 

 Lithagrion being stated: 



2. Probably only two antenodals.^'* 



4. Stigma having its proximal edge very much less oljlique. 

 6. The veins generally, posterior to Mi, have a slighter caudal 

 curvature as they approach the wing-margin. 



12. Between Rs and iVls is only one row of cells to the wing-margin. 



13. Arculus at the second antenodal. ^^ 



156. Between Ms and M4 at the wing-margin are only two or three 



rows of cells. 

 17. Between M4 and Cui are (a) three antenodal cells and (6) one 



row of cells increasing to two rows only at the extreme margin. 



19. Between Cui and Cu: at the wing-margin is only one row of cells. 



20. Area posterior to Cu2 with only one row of cells. 



21. Anal vein, separating from the hind margin of the wing distad 



to the levels (a) of the arculus and (6) of the cubito-anal cross- 

 vein. 



22. Anal cross-veins proximal to the level of the distal end of the 



quadrilateral apparently none. 



12 Scudder's description, p. 136, says, "The wings are petiolated veiy nearly 

 up to the first postcostal nervule, which is placed shortly before the base of the 

 quadrilateral. " 



13 Tertiary Insects of North America, 1890, pi. 13, fig. 4, and pp. 128, 134-136. 



1^ Scudder's figure, I.e., shows but one, at the arculus^ Compare Prof. Cock- 

 erell's statements on this point in Bull. Amer. Mus. Nat. Hist., XXXIII, p. 137 

 (1907); XXXIV, p. 63 (1908); Amer. Journ. Sci., XXVI, p. 69 (1908). 



15 A sketch kindly sent by Prof. Cockerell shows the arculus a little distal to- 

 the second antenodal. 



