HACKBERRY PSYLLIDS. 619 
by its lighter color but furnished in the middle with a moderately long 
spine which is sometimes clavate but readily broken off and often 
lost when the galls attain maturity or in dried specimens. In this 
case there is a more or less conspicuous nipple left in the center of the 
gall. The gall is normally circular iu outline, but often irregular and 
limited by the leaf-nervules. Average diameter, 5 mu \; sculpture coarser 
than, but of the same nature as, that of the leaf. On the under side of 
leaf it is barely distinguishable as a slightly discolored spot, but the 
center rises from a thin base and, spreading out, assumes the form of a 
small flower (resembling somewhat that of a Convolvulus) or a star, and 
this resemblance to a flower is increased by the presence of a small, 
rounded, median nipple, which is often surrounded by a circular rim. 
Average height of this flower shaped excrescence, 1.25 mm ; diameter at 
top, 2.50 mm . The walls of these galls are a little thicker than the leaf 
itself, and, as in the preceding species, the cell is a low chamber with a 
straight roof (i. e., toward the upper surface of the leaf) and the bottom 
a little convex. 
The mature pupa makes its way out through an oval slit always on 
one side of the roof of the gall. 
40 P. celtid is- umbilicus n. sp. — This gall occurs on the upper side of 
the leaf, is regularly circular in outline and abruptly depressed at its 
outer margin beneath the surface of the leaf. From this outer margin 
toward the center the gall gradually rises again to about the level of 
the surface or even above it, the center being furnished with an elon- 
gate nipple (frequently broken off). The color in fresh specimens is a 
little lighter than that of the leaf, but fully developed and dried speci- 
mens are more yellow. Surface opaque, either without any decided 
sculpture, or rugose and with the venation of the leaf still preserved. 
On the under side of the leaf it is distinctly elevated, averaging 2 mm in 
height and 5 mm wide, circular in outline, the sides not abruptly ele- 
vated but gradually rising, with a larger or smaller shallow depres- 
sion at top which is often furnished with a small central nipple. Color, 
yellowish-green in fresh, and more yellow in dried specimens ; surface 
opaque, rugose. Gall woody and hard, the wall at the bottom about 
l mm in thickness ; that of the roof about £ mm . Cell formed as in the 
preceding species, but much larger ; mode of issuing of mature pupa 
also as in the preceding. 
There is no difficulty in recogniziug this gall, especially from its 
appearance on the upper side of a leaf. 
41. P. celtidis-mamma Riley (Johnson's Universal Cyclopsedia, 1876 ? 
p. 425 ; Canad. Ent., v, 15, 1883, p. 158 ; J. Fletcher in Rep. Ent. Soc. 
Ont. for 1882 [1883], pp. 79, 80).— This gall, on upper side of leaf, is 
represented by a very regular cup-shaped impression, measuring on 
the average 4.5 mm across, with the upper, outer rim always regularly 
circular, and not, or but slightly, elevated above the surface of the 
leaf; at the bottom of the cup a small median nipple (often obso- 
lete) ; walls of the impression greenish, the bottom more yellowish. 
