400 PROCEEDINGS OF THE ACADEMY OP 



tip and prolonged on each side not far from the tip in a lateral, horizontal, la- 

 mina, which at first expands gradually in width towards the base, and finally 

 sweeps round in a regular curve inwards to the tip of joint eight, where the 

 sides of that joint close upon it. Legs black, basal half of the anterior femora, 

 and their trochanters yellowish ; the extreme base of the intermediate femora 

 and their trochanters marked with yellowish ; all six coxa? pale, obscure green. 

 Wings hyaline, the anteriors flavescent at their extreme base, and on the costa 

 from about the nodus to the pterostigma; the inferiors flavescent at base, espe- 

 cially next the membranule, and on the costa from inside the nodus to the pte- 

 rostigma ; veins and cross-veins black; pterostigma small, black, surmounting 

 not quite one cell; membranule fuscous, whitish at its extreme base. Antecu- 

 bitals eight, postcubitals six. Discoidal areolets two, commencing always with 

 two. 



Length 9 60 mill. Alar expanse 9 83 mill. Pterostigma 9 1\ mill. Ab- 

 dominal appendages 9 "$\ mill. One 9; d 1 unknown. Joints 8 10 of the ab- 

 domen are each from one-half to one-third shorter than the joint immediately 

 preceding it, joint ten about one and a quarter mill. long. The only difficulty 

 in referring this insect to Say's $ , is the yellowish spot which he speaks of 

 behind the two thoracic vitise ; but the existence of such a spot on the thorax 

 is so contrary to the normal style of ornamentation in odonata, that it is pro- 

 bable that it'was the spot on the base of the abdomen which he inadvertently 

 referred to. Dr. Hagen's $ agrees exactly in the antecubitals and postcubitals, 

 but has only " two obsolete yellow lines" on the pleura, instead of two well 

 developed yellow stripes. Both in Say's $ and in Dr. Hagen's (J 1 , the legs are 

 "black" or "immaculate." 



Epitheca princeps, Hagen, [occurred on the Des Plaines River.] Cordulia 

 lateralis tf 9 Burm. 1 [The tf has the anal angle of the posterior wings 

 acute, and it cannot therefore be an Epitheca.] Pantala hymen^a $ 9 Sa.y ! 

 [occurs both in North and South Illinois; not captured North of Texas since 

 Say's time ; has the same migratory and social habits as Libellula quadrimacu- 

 lala, Linn., but unlike that species never alight9 to devour its prey, and is con- 

 sequently very difficult to capture ] Tramea lacerata, Hagen ! [occurs both in 

 North and South Illinois] Celithemis eponina, Drury ! Celithemis elisa, Hagen. 

 [Referred to Diplazby Dr. Hagen, but I think erroneously. The pair I possess 

 were given me by my friend Mr. A. Bolter of Chicago, at which place he took 

 them.] Plathemis trimaculata, De Geer! [N. and S. Illinois.] Libellcla 

 quadrimaculata, Linn. ! Lib. semifasciata, Burm., [occurred on the Des Plaines 

 River.] Lib. luctuosa, Burm. ! Lib. pdlchella, Drury ! [N. and S. Illinois.] 

 Mesothemis simplicicollis, Say! Mes. corrcpta, Hagen ! [N. and S. Illinois.] 

 Mes. longipennis, Burm. ! Diplax [assimilata, Uhler =] rdbicundula, Say. 

 Dipl. vicina, Hagen ! Dipl. semicincta, Say. Dipl. ambigua, Rambur. Dipl. 

 intacta, Hagen. 



I am satisfied that Diplax assimilata, Uhler, (No. 1 of the Synopsis, and named 

 assimilata for me by Dr. Hagen himself,) is the true rubicundula, Say,and that 

 Diplax No. 6, {ambigua, Rbr.,) is erroneously identified with Say's species. Say 

 describes his rubicundula as occurring sometimes with the basal half of the 

 wings flavescent, which is true of No. 1, but untrue of No. 6. No. 6 positively 

 swarms at Rock Island every year about the last of August, and continues till 

 the frosts come ; and although I have seen millions of specimens on the wing, 

 and have looked out two seasons for such variations, I never yet saw one with 

 the basal half of the wings even subflavescent. Again, Say gives one and a 

 half inch as the length of his species ; now, that is the average length of 

 No. 1, whereas No. 6 averages only about one and a quarter inch, and is constant 

 in size. Mr. Uhler, at the time he published his assimilata, had never, as he has 

 informed me, seen any specimens with perfectly hyaline wings. I forwarded 

 such to him last autumn, and I believe he now inclines to think that my view 

 of the subject is correct. The two species are distinguishable at once by No. 1 

 having both its anterior and intermediate femora posteriorly vittate with yel- 



[Sept. 



