188 
[October 
Two % taken on Rock River, in addition to the one % which I wrongly 
described as a Perla; 9 unknown. But for the difference in the num¬ 
ber of the ocelli, this species might be taken for a variety of C. hrun- 
nipennia Walsh. I do not know whether any other N. A. Chloroperla 
has only two ocelli. C. hilineata Say, and nana Walsh, I know to have 
three, and severa Hagen, is expressly described as having three. As 
nothing is said as to their number in the other 5 described species, we 
may presume that they also have three. It is remarkable that in Per- 
lina the number of ocelli, which elsewhere is of high systematic value, 
becomes scarcely of subgeneric value. Since, however, the species of 
Perla are very numerous, it affords a convenient means of subdividing 
that difficult, polymorphic and extensive genus. 
Nemoura albidipennis. Walker. This species, of which I have 
taken 5 specimens, may now be added to the list of Illinois Perlina. 
It is easily known from N. completa by its wing-veins margined with 
fuscous, and the absence of the two pale fuscous fasciae from the front 
wings. The latter occurs on the Mississippi River, the former in the 
neighborhood of Rock River. 
EPHEMERINA.— BiETis. 
Note 6, p. 169.— BiETis femorata Say, described by Say in the 
subimago only.—Say describes, in all, ten species of Ephemerina, at 
least one of which (i?. ohesa), and most probably one or two others, 
are subiniagos. Yet he nowhere drops a word from which it can bo 
inferred that he knew the difference between the imago and subimago 
states, or that there was such a state as that of subimago.* It is pos- 
* All subimagos known to me may be distinguished from their images by 
the wings being eiliate except on the costa. Sometimes this ciliation can 
scarcely be seen except under the lens, or by holding the wing up to the light. 
Their abdominal setae are likewise always more or less pilose, but this character 
is found also in the images of Bcetis ^ A (Walsh) and Palingenia ^ B (Walsh), 
towards the tip of the seta. On the subimago or pseudimago state see Westw. 
Introd. II, pp. 27—28 and ISTote Westwood here infers analogically that a 
subimaginal pellicle “is to be found in the bee as well as the beetle.” It has 
been actually observed in the Ant by Huber, (quoted in St. Fargeau Hymenopt. 
I, p. 114,) and I have myself recorded it as found on the antennae of a Chalcide 
species, Glyphe viridescens Walsh, {Trans. III. State Agr. Soe. IV, p. 390.) a.nd 
have since observed the same thing in several other Chalcidians. 
