E. heterocaudata McDunnough 1929, male: Middle tail 

 more than twice as long as the outer ones; length of fore 

 wing, 7 mm.; thorax and abdominal tergites olive brown, 

 the thorax darker with dark shadings and markings; legs 

 dark olive with fore femur and tibia tinged with black. 

 Wings hyaline, long veins smoky and cross veins pale. 



E. heterocaudata McDunnough 1929, nymph: Middle tail 



■three or more times length of outer ones; gills on tergites 

 • three to seven; general color dark brown with head blackish 

 and legs without pale bands;dorsal spines large and strong, 

 incurved, becoming progressively longer and further apart 

 from tergites two to seven, but shorter and closer together 

 on eight to nine. Found in Alpine and Plumas counties. 



E. hystrix Traver 1927, nymph: Middle tail one-half again 

 as long as outer ones; length of body, 7 mm.; length of 

 middle tail, 11 mm.; color dark brown, with legs yellow- 

 brown; very prominent spines on tergites two to nine, those 

 'on two close together and straight and those on three farther 

 'apart and directed outward; on four to seven spines are 

 widely divergent, increasing in size to rearward; they are 

 directed laterally and posteriorly and widely curved, each 

 spine beset with coarse spinules from base to tip; on 

 'segments eight to nine spines are stout but shorter and 

 straighter. Found in Inyo, Nevada, Sierra, Mono, and Shasta 

 counties. 



Subfamily CAENINAE 



Key to the Genera 



Adults 



1 



Posterior branch of M in fore wing and intercalary 

 between branches of this vein much shorter than anterior 

 branch, not extending to base of wing; male forceps 

 3-jointed 2 



- Posterior branch of M in fore wing and intercalary 

 between branches as long as anterior branch, extending 

 to base of wing; male forceps 1-jointed 3 



2. Tails 2; fore wing elongate and narrow, broadest in the 

 center Leptohyphes Eaton 



- Tails 3; fore wing broad, widest in anal region (fig. 

 3:24a) Tricorythodes Ulmer 



3. Prosternum twice as wide as long, fore coxae therefore 

 widely separated; second joint of antennae 3 times as 

 long as first Brachycercus Curtis 



- Prosternum 2 to 3 times longer than wide, coxae much 

 closer together; second joint on antennae not more than 

 twice as long as first (fig. 3:10a) Caenis Stephens 



Nymphs 



First abdominal segment without gills; gills of second 

 segment well separated on middorsal line, operculate, 



covering all following gills 2 



First segment bearing tiny single gills; gills of second 

 meet or overlap on middorsal line, operculate, covering 



all following gills 3 



Operculate gills triangular (fig. 3:246, c) 



Tricorythodes Ulmer 



Operculate gills elongate and oval. . Leptohyphes Eaton 

 Three prominent tubercles on head; maxillary and 



labial palps 2-jointed Brachycercus Curtis 



No tubercles on head; maxillary and labial palps 3- 

 jointed (fig. 3:24d,e,f) Caenis Stephens 



Genus Caenis Stephens 



This tiny nymph is from 2 mm. to 4 mm. in length, 

 a lotic form living in the silt of the bottom. 



Besides C. tardata, found in San Diego County, one 

 unnamed species of this tiny, two-winged genus has 



99 

 Day: Ephemeroptera 



been collected in Napa County; tin- undescribed 

 species is rather cloael) related to C. tardata Mc- 

 Dunnough 1931, the male of the Latter being described 



as follows: 



Forceps with one joint unl>, shorl (fig. 3:24 A); head 

 blackish; mesonotum deep brown and abdomen dot I ills 

 black shaded on segments one to .six, entirely pale <>n 

 seven and eight, and faintly dark shaded on nine and ten. 

 All sternites are wholly pale yellowish white. The wink- 

 are 3 mm. in length. 



Genus Tricorythodes Ulmer 



This is another genus with hind wings absent; the 

 species are quite small in size, the wing length being 

 from 3 mm. to 7 mm. Tricorythodes is represented in 

 California by the single species T. fallax Traver 

 1935 which is very widespread in the northern coastal 

 region, the nymph being found in quiet water on the 

 bottom of the stream. Notes on T. fallax are as 

 follows: 



Adult. — Length of fore wing 5-6 mm.; a blackish or brown- 

 ish black species. Entire head, thorax, and abdomen 

 blackish brown, with tergites one, two, eight, and nine 

 black, and blackish markings numerous. All tibiae and 

 tarsi white except the apical tarsal joint which is faintly 

 dark; apex of tibiae narrowly black; tails gray with hyaline 

 joinings (fig. 3:24Z). 



Nymph. — Length of body 3V£-5 mm.; pale whitish species 

 with black surfacing on head, pronotum and abdominal 

 tergites: a black spot at femorotibial knees; tibiae smoky 

 brown, with all other leg joints white. The large, triangular 

 operculate gill on segment two is dark in color. 



Subfamily BAETINAE 



Key to the Genera 



Male Adults 



1. Hind wings present 2 



— Hind wings absent 4 



2. Fore wings usually with numerous costal cross veins 

 before the bulla; hind wings with a moderate number of 

 cross veins, at least in the costal region (fig. 3:24<7) 



Callibaetis Eaton 



— Fore wings without costal cross veins before the bulla; 

 hind wings with no cross veins, or with very few of 

 them 3 



3. Marginal intercalaries of fore wing occur singly (fig. 

 3:24A) Centroptilum Eaton 



— Marginal intercalaries of fore wing occur in pairs (fig. 

 3: 106) Baetis Leach 



4. Marginal intercalaries of fore wing occur singly .... 5 



— Marginal intercalaries of fore wing occur in pairs ... 6 



5. Basal joint of hind tarsus very long, equal in length 

 to the 3 other joints together; second joint of forceps 

 short and broad, its inner margin with a prominent, wide 

 extension Neocloeon Traver 



— Basal joint of hind tarsus only moderately long, equal 

 in length to the third and fourth joints together; second 

 joint of forceps longer and narrower, conical, tapering 

 apically, with no extension on its inner margin 



Cloeon Leach 



6. Fore tibia Vfa to \% times as long as femur . . . .Pseudo- 

 cloeon Klapalek, Paracloeodes Day, Apobaetis Day 



— Fore tibia more than twice as long as femur 



Maetodes Needham & Murphy 



