1863.] 
171 
Eiithoron leiikon^ usually called the White Fly of the Passaik River,” 
in the Trans. Amer. Phil. Soc., (Philadelphia, 1802^ Tom. V., No. 
VII. p. 71—4.) I extracted in London the following description:— 
“ Eyes large and prominent ] ocelli none; wings membranous, reticu¬ 
late ; hind wings one-half shorter, narrower, and covered by the front 
wings; antenn* setaceous, half an inch long, [apparently the anterior 
legs are meant, Hagen^~\ six-jointed and with a basal joint; two anal 
appendages IJ inch long, divergent, with from 15—20 joints; tip of 
the % abdomen with two elbowed claws, Jq inch long, curved inwards. 
Length of the insect J inch; body not thicker than a grain of rye; 
abdomen narrower. Wings, abdomen and legs white, eyes black, body 
fuscous, flight like that of a Libellula. They appear about 15 minutes 
after sundown. The chrysalis is like the imago; the chrysalis appears 
and immediately afterwards the imago appears. The 9 lays two eggs. 
They are as numerous as snow-flakes. Passaik River, N. J., Belville 
Bridge, 2 miles, for 3 weeks after the 20th of July.” 
I think this is the B. alba Say, Hagen, of which I have only seen 
a subimago in very bad condition from the Red River of the North. 
As Dr. Williamson’s data are very precise, one might easily verify the 
species upon the spot. [Nee note 12.] 
The genus Baetis is a difficult one. B. ohesa^ fusca^ dehilis^ nrida^ 
ignava^ fmcata^ invaria^ annulata^ femorata^ luridipennis^ hasalis^ and 
novehoracana^ I have described only from the short descriptions of 
Say, Walker, &c. Of the seven others, B. tessellata^ a poor alcoholic 
specimen, is possibly not a Baetis, and for the six remaining species 
my materials were very slight when I wrote the Synopsis. I have 
received since some very fine Ephemerina from Baron Osten Sacken. 
B. vicaria is different from any species described by Mr. Walsh. 
POTAMANTHUS. 
P. ODONATUS Walsh, {=P. nehidosus Walker.) S imago, Saskatch- 
awan, R. Kennicott, 1860. Head, antennse and thorax above and 
beneath black, highly polished. Abdomen piceous above with paler 
incisures, brown beneath, the incisures paler; anal processes brown; 
penis bifid, apex divaricating; the two exterior setae very robust, brown, 
the incisures darker; the middle seta fine, white, the incisures fuscous, 
alternately wide and narrow on the basal half, uniform behind the 
middle and towards the tip becoming very wide. Anterior legs pice- 
