T D. A. Cocker ell — Descriptions of Tertiary Insects. 69 



Art. VI. — Descriptions of Tertiary Insects / by T. D. A. 



CoCKERELL. 



Part IV. [Continued from p. 312.] 



(9) Dragonflies from I J lorlssant, Colorado. 



Melanagrion nigerrimum sp. nov. 



Wings hyaline basally, to about three cells beyond the 

 quadrangle ; beyond that black to apex (owing to the partial 

 destruction of the membrane, the black is patchy and. irreg- 

 ular ; the apical field was perhaps dark brown rather than pure 

 black) ; first row of costal cells broad, as in lithagrion / at 

 the tenth cell before stigma the costal cell is half size of sub- 

 costal, the latter being twice as deep ; apex of quadrangle to 

 tip of wing about 24rJ Ium (26f in 31. umbratum), but the ten 

 costal cells before stigma measure together about 7J mm (six in 

 31. umbratum). Stigma large, about 3J mm long, bounding five 

 cells below ; costa obtusely bent at stigma, the margin beyond 

 rapidly descending to apex ; eight poststigmatal sectors ; vein 

 Cn 2a a little before medioanal link ; base of wing agreeing in 

 general with 31. umbratum. 



Florissant: one specimen, with reverse; Station 11 ( W. P. 

 Cockerell, 1907). Holotype in Peabody Museum, Yale. 



Lithagrion hyalinum Scudcler. Figure 1. 



A specimen was obtained by Mr. S. N. Rohwer at Station 

 17, on a slab with Typha lesquereuxi Ckll.,* showing some 

 characters heretofore obscure. There are certainly only two 

 antenodal sectors. The stigma is swollen, and bounds 3J cells 

 below. The total length of the wing is 28 mm ; from nodus to 

 stigma 14f mm ; nodus to base 9 mm ; breadth of wing in middle 

 7 mm . These dimensions are uniformly less than in Scudder's 

 type, but that was probably an upper wing, while ours is appar- 

 ently a lower ; there may also be a difference of sex. (In 

 Enallagma civile, male, I find anterior wing 19f mm , posterior 

 1SJ). There are 17 sectors on costa between nodus and stigma 

 (16 in type L. hyalinum), and 11 in the same distance in the 

 subcostal series ; the costal cells beyond the stigma are doubled, 

 which is not at all the case in Melanagrion nigerrimum (in 

 31. umbratum there is a slight tendency to doubling). There 

 are three simple cells^between ~M 1 and M 2 before the doubling 

 begins. 



These new materials make the genus Melanagrion appear 

 less distinct than when it was proposed, 31. nigerrimum being 

 in some respects intermediate between Melanagrion and lith- 



* On the other side of the slab is Planorbis florissantensis Ckll. (Peabody 

 Museum, Yale). 



