May, 1953 
26. STERLING: at light, May 21-22, 1925, 
D. H. Thompson, 5 2. 
12. LEPTOHYPHES Eaton 
Leptohyphes Eaton (1882: 208). 
This genus formerly was thought to be 
restricted to South America and Central 
America; I have, however, seen specimens, 
referable to Leptohyphes, which were col- 
lected at lights in San Antonio, Texas. 
Species of the genus Leptohyphes consist 
of small or medium-sized, fragile mayflies 
which closely resemble the other members 
of the family Caenidae. The fore leg in the 
males is shorter than the body, and the 
hind leg is slightly longer than the fore leg. 
The fore wing is constricted in the cubito- 
anal region, as in mayflies with two pairs of 
wings; veins R, and R, diverge at or near 
the center of the wing, and vein M, and the 
median intercalary vein arise at a point some 
distance distad of the wing base. The hind 
wing, persisting in the subimagoes, usually 
has a very long, thin costal projection; there 
always is a pair of thin, membranous pro- 
jections arising near the wing bases and ex- 
tending along the lateral margins of the 
mesoscutellum. The male genitalia consist 
of a pair of 3-segmented forceps and a pair 
of slender, apically diverging penis lobes. 
There are two long caudal filaments; the 
middle one is vestigial. 
In the nymphs, which are flattened and 
sprawling forms having relatively short, 
thickset legs and edentate claws, the pro- 
notum typically is rectangular, with the an- 
terolateral angles acute. Two pairs of 
wingpads are present. The abdominal gills 
are borne at the lateral margins of segments 
2-6; the first pair is elongate-oval and 
elatroid, covering the following pairs of 
gills; the lateral margins of the abdominal 
segments are produced as broad, shelflike 
projections having the posterolateral angles 
acute. There are three well-developed 
caudal filaments. 
EPHEMERELLIDAE 
The family Ephemerellidae, as it is here 
treated, is identical with the subfamily 
Ephemerellinae of the family Baetidae of 
Traver (1935a:562) or the family Ephem- 
erellidae of Ulmer (1933:204). In my 
opinion, this group of mayflies is sufficiently 
Burks: THe Mayr tirs or ILLINoIs 55 
different from all others to require segre- 
gation as a distinct family. The ephemerel- 
lids are quite a homogeneous group and as 
far diverged from the fossil ephemerid pro- 
totype (Tillyard 1932) as are the Ephemer- 
idae or Heptageniidae. It may be noted that, 
although the ephemerellids are world-wide 
in distribution, they were first recognized as 
a distinct group by Walsh in 1862, on the 
basis of a study of specimens he had collected 
at Rock Island, Illinois. 
Although ephemerellids are one of the 
commonest mayfly groups in the northern 
and western states and are represented 
there by a large number of interesting 
species, they are relatively uncommon in 
Illinois. They seem to require for their 
development either somewhat rapid, clear 
streams which are cool throughout the year 
or small, clear lakes. Such bodies of water 
are rather rare in this state, but a few suit- 
able habitats are provided by Nippersink 
Creek in McHenry County, the Rock River 
in Winnebago and Ogle counties, the Kan- 
kakee River in Kankakee County, the Salt 
Fork River in Vermilion County, Lusk 
Creek in Pope County, and some of the lakes 
in Lake County. A few ephemerellids have 
been taken in the Wabash River at Mount 
Carmel, but, in general, the Wabash River 
does not provide a habitat favorable for 
their development. They seem to have 
disappeared completely from the Mississippi 
and Rock rivers at Rock Island, although 
they obviously were fairly common there in 
the early 1860’s when Walsh collected and 
described the genus Ephemerella and two 
species from that locality. 
The ephmerellids offer an excellent ex- 
ample of a common mayfly phenomenon: 
the nymphs are more easily collected and 
more readily separated to species than the 
adults. The nymphs can be found at almost 
any time during the spring or summer 
months by turning over rocks and debris 
in the streams or lakes in which they live. 
The adults have a length of life of only 3 
or 4 days, are strong fliers and rather difh- 
cult to net, and have a high mortality rate 
when being reared from the nymphs. Oppor- 
tunities for obtaining adults of a given 
species are thus relatively few. As a con- 
sequence, most American mayfly collections 
include a great many more nymphal than 
adult specimens of ephemerillids. The 
Illinois Natural History Survey collection, 
