1863.] 
203 
rafts come from various rivers which empty into the Mississippi, it 
happens, as we might a priori anticipate, that from time to time new 
Ephemerinous species are imported amongst us. This may account for 
the fact, that although in 1862 I pretty thoroughly explored the neigh¬ 
borhood of our saw-mills, yet in 1863 I have met with several species in 
considerable abundance which were previously unknown to me. On 
the other hand, of several species that were abundant in 1862, I have 
in 1863 met with only one or two specimens, e. g., Potamanthus cupi- 
dus, Bsetis alterwita and Bsetisca ohem. —This may, however, be partly 
explained by the fact that in 1863 the Mississippi has been unusually 
low and comparatively but few log-rafts have come down. 
P. PULCHELLA Walsh, and P. terminata Walsh. I am not sure 
but these two species are identical. I had supposed that the pre¬ 
sence of fuscous dots in pulcliella^ located on the spiracles of the pale 
segments of the abdominal dorsum, was a constant character % 9 ; but 
out of many dozen individuals examined in 1863, I find a % with these 
dots subobsolete and another with them obsolete. AXihovL^h. pulchella 
has been abundant in 1863, I have not seen a single terminata^ so as 
to determine with precision the color of its eyes. Pulchella certainly 
has them “ pearly-whitish,” and from my general recollection that the 
eyes of terminata were yellow, I stated them in my description 'to be 
“ generally yellowish.” In this, however, I may possibly be mistaken, 
for I was not in the habit in 1862 of noting the color of the eyes in 
the field, and these organs often turn black in the interval between 
capture and death, sometimes both, and sometimes only one. The 
only constant distinguishing character that remains is, that the four 
hind legs and the abdominal joints 1—^6 are pure whitish in pulchella 
and pale yellowish in terminata^ which, unsupported by a constant and 
decided difierence in the color of the eyes, would not be sufiicient to 
separate such closely allied species. Here, as elsewhere, it is easy to 
separate two individuals, but to separate two species, when specimens 
are greatly multiplied, is a far more difficult undertaking. 
As to Hr. Hagen’s remark on the probable identity of P. 'pulchella 
Walsh, and Baetis verticis Say, there is some clerical or typographical 
error in the figures given in the Synopsis. Say says that B. verticis 
is “ over one-fourth of an inch long,’’ and the setae “ over three-tenths,” 
which in millimetres would be about 7 and 8 ; and he says likewise 
