of certain species of Willow. — Part 2nd. 277 



making Euura s. ovum n. sp., which inhabits a certain well-characterized 

 Willow-gall. (See above, p. 254). 6th and lastly. In the case of Cynips 

 q. sponyifica 0. S. and C. q. inanis 0. S., the £ 9 gall-making irnagos, 

 produced in the same month of the year from very distinct galls occur- 

 ring exclusively on very distinct Oaks, cannot be distinguished in any 

 way from one another when placed side by side, as both Osten Sacken 

 and myself have clearly ascertained.* 



The general rule with all gall-making insects seems to be, that each 

 particular species is confined to one particular species of the genus or 

 genera of plauts, inhabited by the particular genus of insects to which 

 it belongs. But there are very numerous exceptions to this rule; and 

 those in the family Cynipi<tse will be found collected together in the 

 first part of this Paper, where it is shown that even then the Cynips 

 always restricts itself to one or other subgenus or section of the botani- 

 cal genus Quercus. (Pp. 638 — 9, note ; see also Osten Sacken's fourth 

 Memoir on U. S. Cynipidze, Proc. etc. IV, p. 342.) Now it is a most 

 remarkable fact, that in all these cases, so far as known to me — and I 

 could now add some others to the list — the galls, although they occur 

 on different Oaks, are absolutely undistinguishable ; and under similar 

 circumstances the same thing is true, so far as my experience extends, 

 of Cecidomyidous galls, "{"of Aphidian galls. J of Tenthredinidous galls, || 



* The specific distinctness of these two Cynips has been questioned by Dr. 

 Eeinhard of Germany, but I hope to prove it in a second Paper on Dimorphism 

 in Cynipidoe. Dr. Reinhard's suggestion is that they may both of them be in- 

 quilines, belonging to the same species. 



-j- Galls S. strobiliscus Walsh, (doubtful) on Salix rostrata and S. discolor: S. 

 nnnj,halioides Walsh on S. humilis and S. discolor: S. siliqua Walsh on S. humi- 

 lis, S. discolor, S. rostrata, S. cordata and S. petiolaris : S. batatas Walsh on S. 

 humilis, S. discolor and S. cordata (?) : S. verruca Walsh on S. humilis and S. 

 discolor: and a precisely similar gall on Solidago (sp. ignot.) and Vernonia fasci- 

 culata producing from each Lasioptera solidaginis 0. S., which may, however, pos- 

 sibly be an inquiline and not a gall-maker. (See above, p. 273.) 



\ Gall vagabunda Walsh, on Populus angulata and P. balsamifera. The Hic- 

 kory galls caryacaulis Fitch, cai-ysefoliai Fitch and carya? globuli Walsh (all 

 three formed by Aphidians) occur, so far as I have observed, locally and abun- 

 dantly on the Shag-barked Hickory, (Caryse alba,) and scarcely ever on the 

 Fignut Hickory, (C. glabra,) but on whichever species of Hickory they occur, 

 they are exactly alike. The gall ulmicola Fitch (which I have shown 

 to be made by a Thelaxes f) occurs, so far as I can perceive, only on the White 

 Elm, (Ulmus americana,) or, as I incline to believe, on an undescribed species 

 of Elm, which has a leaf intermediate in roughness between those of the White 

 and Red Elm, (U. fulva,) never exceeds 25 or 30 feet in height, has a much 

 more upright habit than either the White or the Red Elm, has timber easily 

 split, instead of remarkably tough and loeky as in the case of the Whit<- Elm. 

 and is popularly known in the West as " Hickory Elm." The case of an Aphi- 



PnoCEKDIXGS EXT. SOC. PHILAD. JANUARY, 1867. 



