216 E. B. WILLIAMSON. 



minutus, 1-0 ; quadricolor, 1-0 ; descriptus, 4-1 ; vindijrons, 2-1 ; 

 pulchellm, 1-1 ; brevis, 7-21 ; grasiinellus, 0-1. 



On the basis of the ratio of the number of wings like fig. 4 (or 

 4a), plate viii, to the number like fig. 5 (or 5a), species 17-27; in- 

 clusive are arranged as follows: villosipes, 18-6; crassus, 11-12; 

 externus, 4-7; spiniceps, 6-11; fraternus, 13-42; scudderi, 4-14; 

 plagiatus, 12-72 ; notatus, 4-36 ; vastus, 1-31 ; dilatatus, 0-2 ; am- 

 nicola, 0-12. 



EXPLANATION OF PLATE VIII. 



Figs. 1-6. — Postanal cells of left hind wings of : 1, G. furcifer ; 

 la, G. pulchelhis ; lb, G spicatus ; Ic, G. pulchellus ; Id, G. brevis; 

 2, G. vulgatissinius ; 3, G. simillimus ; 3a, G. brevis ; 4, G. villosi- 

 pes ; 4a, G. crassus; 5, G. fraternus; 5a, G. plagiatus; 6. G. albi- 



stylus ; f. /, first branch of anal vein ; s. - - - 6', second branch 



of anal vein ; s', point where vein separating the first and second 

 postanal cells meets the second branch of the anal vein ; /. pa. first 

 postanal cell ; s. pa. second postanal cell ; -s\ e. portion of anal vein 

 bounding first postanal cell ; i. e. portion of second branch of anal 

 vein bounding first postanal cell. 



Figs. 7 and 8. — Gomphus amnicola Walsh. Rock Island, Illi- 

 nois, Type 1010, U. S. Nat. Mus. Right second hamule, profile 

 (7) and posteriolatero-interaal (8) views. 



Fig. 9. — Dorsal view of the male abdominal appendages of Gom 

 phus notatus Rambur. Ironton, Ohio, June 1, 1899. R. C. Osburn. 



Fig. 10. — Same of Gomphus plagiatus Selys. Sandusky, Ohio, 

 July 6, 1899 ; R. C. Osburn, collector. E. B. AVilliamson. 



Fig, 11. — Same of Gomphus amnicola Walsh. Bethlehem, N. 

 Y., July 6, 1870; Lintner collection. M. C. Z. 



Fig. 12. —Same of Gomphus scudderi Selys. Russell Stream, 

 Northeast Carry, Maine, August 29, 1899 ; F. L. Harvey, collector. 

 E. B. Williamson. 



Fig. 13. — Same of Gomphus spiniceps Walsh. Ohio; J. S. Hine, 

 collector. U. S. Nat. Mus. 



Fig. 14. — Occipital crest of female of Goinjjhns notatus Rambur. 

 One of the types of G. fluvialis Walsh. Rock Island, Illinois, 

 Type 1009, U. S. Nat. Mus. 



Fig. 15. — Same of Gomphus plagiatus Selys. Sandusky, Oliio, 

 July 10, 1899. R. C. Osburn. 



