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galls, according to the plant upon which it establishes itself, or that 
a species may even vary with the plants on which it lives, it has 
seemed to me, all things considered, best to affix names to some of 
the forms which I have noticed. I find that the size of the adults, 
the number of transverse striz about the body, the number of prongs 
of the feather-like tarsal appendage, and in some measure the form 
of the body, afford what seem to be characters of specific value. 
Color may also in some cases be characteristic, but I find little 
variation in that respect. In the United States but three species 
have hitherto been indicated by name, one by Dr. Henry Shimer, 
another by Prof. T. J. Burrill, and the third by Mr. Wm. H. Ash- 
mead. Prof. Burrill considers the species observed by him to be 
specifically identical with the Phytoptus pyri of Europe (the mite 
which causes the pear-leaf blister). The mites and galls described 
below comprise but a small portion of those which occur in this 
country, or even in that part of Illinois in which most of them were 
found. Others have been noticed from time to time, when the work 
upon which the writer was engaged would not permit his giving 
them attention. I can say for the South Atlantic and Middle States 
that these mites are decidedly common there, and I have little doubt 
that the Phytoptus galls of the United States will number several 
hundreds. 
Phytoptus abnormis, n. sp. 
Produces galls on the leaves of the American linden or basswood, 
Tilia americana, Linn. 
The transverse striz of the abdomen number about 56. This mite 
differs from all the other Phytopti I have seen in that the abdomen, 
just before the terminal sucker,is noticeably enlarged. But few speci- 
mens have been examined, as they have been very rare. In many 
of the galls, comparatively large, elongate eggs occur, which pro- 
_ bably belong to some larger mite which preys on the gall-mites. 
The gall is top-shaped, expanding above and contracting towards 
the upper surface of the leaves into a neck. It measures .155 inch 
in height, and .100 inch in diameter. The walls are deeply infolded, 
sometimes giving rise to unequal lobes. The outer surface is smooth, 
green and devoid of hairs. The cavity of the gall is made unsym- 
metrical by the deeper impressions of the wall. The inside of the 
latter is slightly roughened by small folds, and is clothed with long 
aciculate, unicellular hairs. These galls occur, sparingly on the 
leaves of large trees in open woods at Bloomington, Illinois. 
Phytoptus, sp. 
pe coduees galls on the leaves of the poison ivy, Rhus toxicodendron 
inn. 
The gall of this species is a small rounded elevation on the upper 
side of the leaf, having the usual opening below. It frequently covers 
the greater part of the upper surface; and in such cases the indi- 
vidyal cecidii fuse and form granulate heaps, with a common open- 
ing below.. On some of the leaves the galls are purple and 
pubescent, on others they are yellowish-green, and have very little 
pubescence. The inside is clothed with white hairs. Galls of this 
