192 
[October 
are pale on their basal halves. The coloration of the anterior legs in 
both arida and sicca is so variable that it is difficult to fix it definitely 
without being unduly diffuse. To describe the individual is always 
easy; to describe the species^ “ hoc opus, hie labor est.” 
Note 11, p. 170. The difference between arida and sicca in the 
coloration of the setae prevails only generally, not universally. In many 
other Ephemerina the setae are sometimes immaculate, sometimes incised 
with fuscous, the more immature individuals having immaculate setae 
like the subimago; e. g., Palingenia interpunctata and P. jlavescens 9 . 
The more constant differences between arida and sicca may be thus 
tabulated from a careful comparison of numerous additional specimens; 
it is seldom that closely allied species can be so sharply separated. 
Bjetis arida Say, Walsh. 
Bjetis sicca Walsh. 
Dorsum of abdominal 
joints 1—8. 
Piceous % , dark ferrugi¬ 
nous 9> with lateral 
basal pale ferruginous 
triangles or semicircles 
both % and 9 • 
Piceous % , dark ferrugi¬ 
nous 9 j immaculate. 
Last abdominal dorsal 
joint ^ 9 . 
Pale ferruginous. 
Piceous % , dark ferrugi¬ 
nous 9 • 
Abdominal setse 9 • j 
Pale greenish white, im¬ 
maculate. 
Pale greenish white, with 
slender fuscous incis¬ 
ures, sometimes obso¬ 
lete except at base. 
Cross-veins of the an¬ 
terior wing %. 
Pale greenish hyaline. 
Fuscous. 
Veins of the anterior 
wing %. 
Pale greenish hyaline, 
sometimes tinged with 
fuscous towards the 
costa. 
Fuscous. 
1 
In both species there is a narrow fissure between the eyes % sub¬ 
imago when recent, which is absent in the imago. I was mistaken in 
supposing this fissure to be peculiar to arida^ and I have observed the 
same character in the subimagos of some other Bmtis. My observa¬ 
tion on the comparative shortness of the % front legs in sicca is only 
generally, not universally true. Individuals occur with the front legs 
as long as the body, and I have one now before me with the front legs 
