1864.] 
493 
am familiar with the gall q. tuber Fitch, and it is quite different from 
q. podagrse^ besides that it grows exclusively on the White oak. The 
gall q. arhoH Fitch, is described as growing exclusively on the tips of 
the limbs of aged White oaks. The gall q. bafatus Fitch, also occurs 
on the White oak and somewhat resembles q. podagrse, but the fly is 
described as having its legs “ dull pale yellow ” and all its thighs 
“black,’’ and besides its antennae are 13-jointed9, not 14-jointed. 
Most probably, as shown above, pp. 464-5, the flies of all these three last 
galls described by Dr. Fitch, are guest gall-flies and not true gall-flies. 
GrUEST GALL-FLIES, Si/nevges rhnditiformis n. sp. and S. mendax 
n. sp. See below. Both species came out between May 10 and 15, 
3 or 4 weeks after the first G. q. podagrse and from the same galls. 
14. White oak. Grail tuber Fitch. Described and figured W. Y. 
Rep, IT, §309. Dr Fitch says that “a single gall always suffices to 
kill the limb at and above the point where it is situated,” and observes 
that there are two distinct varieties, one “ growing upon the ends of 
the limbs” and another “lower down upon their sides.” Near Bock 
Island the recent galls always grow upon the tips, never at the side, of 
twigs, and frequently the twig is not killed by it and growing out of 
the tip of the old gall closes over the perforation made by the Cynips, 
and presents the appearance of having a recent gall upon its side in¬ 
stead of at its tip. The knife speedily dispels the illusion. 
GtALL-fly, unknown ? I have never bred from.these galls. 
verse vein which Osten Sacken notices as a constant character in Rhodites 
hicolor Harris; others again are without it. I suspect that, like spongifica and 
inanis, podagrce a^xidi punctata are distinct races of the same species, which have 
acquired a habit of exclusively attacking the Black oak or the Eed oak; in 
other words, that they are what Mr. Darwin would call “ incipient species.” 
Probably in the course of a few thousand years other distinctive characters, 
besides the coloration of the abdomen, will by the laws of Variation and Inher¬ 
itance be gradually produced, and they will then become distinct species. 
It is possible, however, since only the 9 9 of these two forms are at present 
known, and since those 9 9—from the great numbers reared both by 
Mr. Bassett and myself without a single % amongst them—are perhaps the 
secondary dimorphous 9 forms corresponding to aciculata, that either the pri¬ 
mary dimorphous 9 forms corresponding to spongi/ica, or the b 'S > or both of 
them, may differ so much from each other that podagroe and punctata must be 
considered as distinct species. Hence it will be advisable for the present to 
treat them as provisionally distinct.—March 21, 1864. 
