416 Annals Entomological Society of America [Vol. V, 
occur on the anterior and posterior annuli of each. Two groups of 
setee occur on the dorsal aspect of each posterior annulus. The entire 
‘surface of the first seven abdominal segments, excluding the interseg- 
mental grooves and the constrictions, are thickly studded with fine 
brown chitinous spines. The eighth, ninth and tenth abdominal seg- 
ments bear, on the dorsal surface, nine chitinous plates, one on each 
annulus. These plates are brown, heavily chitinized, and transversely 
elongated. They are not uniform either in size or shape, but in general 
the nearer the caudal region the larger do they become. The plates on 
segments nine and ten are approximately constant in size and shape in 
the different specimens, but in segment eight there is some variation. 
Usually three plates are present, but occasionally a specimen is found 
in which one may be very diminutive, or even entirely lacking. The 
plate on the posterior annulus shows the greatest variability. In 
exceptional cases it may be entirely absent, but the common form of the 
variation is in the size and shape. Judging from the predominance of 
the specimens showing it, the common form seems to be a central, 
somewhat quadrate plate with a small circular plate on either side. 
Other specimens may show the middle plate reduced to the size of the 
two small lateral ones. Still others show one of the lateral plates appar- 
ently fused with the central piece, and finally, specimens were examined 
in which the lateral plates were absent and the middle plate well devel- 
oped. It seems probable that the latter has come about by the complete 
fusion of the two lateral plates to the median. 
The terminal (eleventh) segment is smooth, heavily chitinized, and 
tapers caudad. The tip is emarginated. It bears two dorsal projections 
which show a few strong bristles; also two ventral projections, longer 
than the dorsal. Each of the four projections is armed at the extreme 
end with a crown of strong bristles. The anal opening is on the ventral 
side of segment eleven and near its base. The opening occurs on an anal 
papilla which is composed of four lobes. The region immediately sur- 
rounding the papilla is not chitinized, but close behind it is a lunate 
chitinous plate. Several long sete: occur near the papilla. 
This larva differs distinctly from that of Ps. schizura in 
length and in diameter, in the number of chitinous plates on 
the dorsal posterior part of the abdomen, and in the presence of 
eye spots. It differs from the larva of Ps. floridica in the annu- 
lation of the body, in the number of setz present and in the 
number of dorsal abdominal plates. The larva of Ps. domestica 
differs chiefly in the length and in the number of dorsal thoracic 
and abdominal plates. The larva of Ps. nocturnala differs 
principally in the form of the body and the number of dorsal 
abdominal plates. 
THE PUPA. 
(bigsanleezene hXexexdr) 
The pupa rests on the sides of the filter stones, often com- 
pletely surrounded by sludge with only the breathing tubes 
