618 FIFTH REPORT OF THE ENTOMOLOGICAL COMMISSION. 
tin* entire cavity of the outer shell. The number of these cells varies 
according to the size of the gall, but is rarely reduced to a single one. 
The full-grown pupa always leaves the gall through the apical open- 
ing, and in doing so has to saw its way out through the top of the inner 
core. 
The gall usually occupies the entire petiole, but in rare instances a 
small portion of the latter is visible between the gall and the twig. 
37. P, (Wastophysa) celtidis-gemma Riley. — This gall is briefly re- 
ferred to but not named by Osten Sacken (1. c, pp. 422, 423.) It is 
much smaller than the preceding, very variable in size, and of irregu- 
lar shape, but always bud like, and looking as if formed by the con- 
glomeration of a number of rounded nodules which are separated from 
the adjoining ones by shallow furrows. Color varyiug from light red- 
dish-brown to dark brown or the color of the twig; surface of the 
young gall usually covered with a dense matting of white woolly hairs, 
which iu the more mature gall are more or less completely lost. Ajb in 
the preceding species, the gall is hard and woody, but entirely closed. 
It is usually opaque, rarely a little shiuiug, the surface indistinctly 
sculptured, but occasionally roughened by adhering particles of the 
scales of the original bud. It has no inner core, and the cavity is 
entirely filled with the cells, which vary from one to eight iu number. 
The outer wall is never more than one millimeter thick, often less, while 
the walls dividing the cells are sometimes very thin and sometimes even 
thicker than the outer wall. The gall occurs only on one-year-old twigs, 
and is formed by the young larvae settling on and sinking into such 
buds as would normally produce a new twig the ensuing year. Each 
mature pupa saws its way through the wall of the gall in spring and 
changes to imago immediately after issuing. 
38. P. celtidis-vesicidum n. sp. — This gall appears upon the upper side 
of the leaf merely as a flat blister of yellowish or reddish-yellow color 
and of irregular outline. It is generally rounded, but often influenced 
and limited by the larger leaf nerves, which are rarely crossed by the 
gall. On the under side of the leaf the gall is still less conspicuous, 
and is visible only as a discolored spot with a small rounded nipple in 
the center. The sculpture of the surface of the gall is the same as that 
of the leaf, and the walls are not thickened. 
This gall often occurs in very large numbers on one and the same 
leaf, crowding one another, and often confluent. The full-grown pupie 
break through the wall of the gall either on the upper or lower side of 
the leaf. The species is most readily recognized from the very incon- 
spicuous appearauce of the gall, and more especially from the fact that 
it is the only one which is hardly developed on the under side of the 
leaf, whereas all the other leaf-galls assume there a more or less con- 
spicuous form. 
39. P. celt idis-aste rise us u. sp. — This gall, on the upper side of the leaf, 
is very similar to the foregoing species, t. 6., represented only by a barely 
raised, blister-like spot, distinguished from the surface of the leaf mainly 
