NATURAL SCIENCES OP PHILADELPHIA. 



393 



The 9 h a s a short, robust, conical black thorn at each extremity of the ver- 

 tical vesicle, rising about as high as the ocellus does. The upper edge of the 

 occiput is bent forwards in the middle, so as to appear emarginate when viewed 

 obliquely from above; in one somewhat immature specimen the central lobe 

 of the labium is yellow ; in another specimen the tip of the intermediate femur 

 is posteriorly yellow. All my 9 specimens have, in addition to the prothoracic 

 spots of <3\ a small additional transverse spot, occupying only the middle 

 of the posterior prothoracic lobe. The earlets (oreillettes) are subobso- 

 lete. The abdominal appendages black, pubescent, half as long again as the 

 last abdominal joint, wide apart at base, cylindrical, slender, very slightly 

 curved downwards, acute, surmounting a transversely semioval anal process, 

 which only extends to one-half their length. Vulvar lamina black, polished, 

 more than half as long as the ninth segment, elongate-conical, curved upwards, 

 contracted in its middle, with a deep, longitudinal suture, its tips bifid and 

 approximate. Antecubitals 13 16; postcubitals 11 13. 



Length J 4 53 55 mill. ; $ 53 55 mill. Alar expanse $ 60 67 mill. ; 9 

 63 72 mill. Pterostigma $ 9 about 3 J mill. Described from eleven ^, three 9- 



There exist in the United States three distinct, but closely allied species, 

 representing the Gomphus vulgatissimus of Europe, the third one of which is 

 now for the first time described. The first is the G. fraternus of Say; the se- 

 cond the G. adelphus of Selys. What is very remarkable, they are all three of 

 them nearly alike in the shape of the superior $ abdominal appendage, and unlike 

 their European prototype in that important character, which is usually different 

 in every different species. In vulgatissimus it is much more robust than in vas- 

 tus, and when viewed laterally it is obliquely truncate at tip below, without any 

 inferior thorn. (See Monogr. p. 131 and Plate VII., fig. 6.) In our three species 

 ii is as I have described it in vastus. As the three resemble each other very 

 closely, it may perhaps be useful to tabulate their principal differences. 



Average length 

 Thorn at each end of ) 

 9 vertical vesicle* J 



Front, anterior surface 



Back of occiput 



Spot, behind eyes 



Posterior prothoracic ) 

 lobe J 



Dorsum of 8th ab- ) 

 dominal segment J 



8th abdominal segment 



Expanse of 8th ab-7 

 dominal segment J 



Width of 8th ventral > 

 segment f 



Vulvar lamina of $ 

 Length of pterostigma 



6. fraternus. 



56 millimetres 



Long.s lender, yellowish 



Yellow 



/Yellow, black at the 

 \ sides 



( Three, yellow, often 

 ( confluent 



Entirely yellow 



A basal yellow vitta 



f Yellow at base on the 

 \ lateral margin 



4| millimetres 



2J millimetres 



("Obtuse at tips and"| 

 < curved strongly > 

 (. outward J 



About 31 millimetres 



G. vastus. 



54 millimetres 

 Short, robust, black 



(Yellow, banded with 



{ black 

 Yellow, black at the ) 



sides J 



Two, yellow, never ^_ 



confluent 



("Black J, only cen 

 < trally yellow i 



I ? 

 Black 



'} 



("Yellow at base on"| 

 < the lateral sub- V 

 (_ margin J 



7 millimetres 



3 millimetres 



I Acute at tips, and "| 

 curving moderate- ! 

 ly upwards, tips f 

 approximate J 



About 3 millimetres 



G. udelpkus. 



(From ''Monogr.," 



p. 414.) 



43 millimetres 



Yellow ? 



All black 



* * * 



* * * 



f A basal yellow 

 ( vitta, semiobsolete 



Entirely black 



* 



* * 



$ unknown 

 2 millimetres 



* I have myself observed this curious character to exist always in $ Gomphus fraternus, Say, 

 in 9 G.fluvialis. m\hi. in <j? G. amnicola, mihi, and also in $ Macrogomphus ? spiniceps, mihi, 

 but never in the tf of the first three species, of which alone I possess the <?. In $ G. grasli- 

 nellus, mihi, it is obsolete. It has likewise been described in the "Monographic" as existing 

 in $ Gomphus spinosus, and, as before stated, in $ Macrogomphus parallelograma and in $ M. 

 annulatus ; and in the descriptions of the J jof these same three species, no mention is made 



1862.] 



