May, 1953 
Illinois Records.—Herop: May 23, 1946, 
Ross & Mohr, 16, 12; June 20, 1940, 
Mohr & Riegel, 16, 2 N; July 16, 1947, 
L. J. Stannard, 1¢. 
23. TRAVERELLA Edmunds 
Traverella Edmunds (1948c: 141). 
Mayflies of this genus are medium sized 
and rather heavy bodied. They are strik- 
ingly marked with contrasting snow-white 
and very dark brown areas. The upper por- 
tion of each compound eye in the males is 
extremely broad and is set off from the 
lower portion by a rudimentary stalk. Two 
prominently projecting lobes beneath the 
frontal shelf of the adult head probably are 
the rudimentary maxillae. The fore tarsus 
in the males is shorter than the fore tibia. 
The wings in adults of both sexes are slightly 
cloudy and tinged with gray-brown so that 
they look somewhat like subimago wings. 
The veins and crossveins, fig. 192, are well 
marked and usually dark brown. The pos- 
terior branch of the outer fork (vein R,) in 
the fore wing is bent rearward near the 
base; vein M, diverges from M, near the 
center of the wing; there are two long, 
cubital intercalary veins; vein Cu,, near the 
middle, is obliquely bent toward the anal 
wing margin. The hind wing has a long, 
acute costal angulation, and vein Sc ends 
at the distal angle of this projection. 
In the male genitalia, the base of the 
forceps is undivided but bears a median 
tooth, fig. 216, and a pair of slender lateral 
processes which lie beside the penis lobes. 
The penultimate segment of each arm of the 
forceps is small and semiquadrate; the apical 
segment is minute and subtriangular. Each 
penis lobe has one long, slender appendage. 
In the females, the terminal abdominal ster- 
nite projects rearward past the bases of the 
caudal filaments, and its posterior margin 
has a deep, median indentation; the eighth 
sternite has a median, membranous structure 
which is eversible and undoubtedly serves 
as an ovipositor. The three caudal filaments 
are subequal in length in both sexes. 
In the nymphs, the body is flattened and 
the head is quadrate and hypognathous. 
The labrum is flat and greatly developed, 
being fully one-third as long as the head. 
Each of the three-segmented maxillary palps 
is held in such a position that it projects 
laterally from beneath the head, the second 
Burks: THe Mayr ties or ILLinotrs 97 
segment resting parallel to the lateral margin 
of the head. The apical palpal segment bears 
a dense brush of long setae. Each labial palp 
has three segments. Each antenna is almost 
twice as long as the head. ‘The tarsal claws 
are relatively short, with a single row of 
denticles on the ventral side of each. The 
gills on abdominal segments 1-7 are all of 
the same type, decreasing in size from the 
first segment to the seventh. Each gill is 
bifid, and each element is lamelliform, with 
the margins finely dissected. Each of the 
three caudal filaments is as long as the body. 
This genus includes only two known Ne- 
arctic species: albertana (McDunnough) 
(19316: 82), occurring in Utah, Saskatche- 
wan, and Alberta, and presidiana (‘Vraver) 
(1934: 199), described from Texas. 
BAETIDAE 
The family Baetidae, as here defined, 
corresponds to a combination of the Baetidae 
of the Baetoidea and the Siphlonuridae of the 
Heptagenioidea in Ulmer’s classification 
(1933), and the name is used in a consider- 
ably more restricted sense than by Traver 
(1935a: 427). 
The eyes in the males are large, figs. 241, 
255-257, and, in many species, each eye is 
divided into two distinct sections: a lower 
portion composed of relatively small facets 
and an upper portion composed of larger 
facets. In eyes that are divided, the upper 
portion of each eye is set on a platform which 
completely separates it from the lower por- 
tion, fig. 257. The wing venation in the 
various members of this family varies from 
a type approaching that of the fossil Permian 
mayfly, Protereisma, to a much reduced type 
in which many longitudinal veins and cross- 
veins have been eliminated. Parts of veins 
may also be atrophied in the wings with re- 
duced venation. This partial atrophy of 
veins is usually evident toward the bases 
of the wings. The hind wing in the various 
genera may be either well developed, or 
reduced in size and venation, or wanting en- 
tirely. The hind tarsus in the adults of both 
sexes have three or four clearly differen- 
tiated segments. 
The male penis lobes vary from a well- 
developed type with relatively complex struc- 
ture, as in figs. 242-246, to a greatly re- 
duced, almost structureless type, as in figs. 
267-269, in the most simplified genera, such 
