48 EEV. A. E. EATON ON EECENT EPHEMEllID^ OR MAYFLIES. 



Section 3 of the Genera. — Type of Ephemera. Adult. — Wing-neuration complete and 

 plentifvil ; in the fore wing the subcosta is displayed, the anal (8) is unequally sinuous, and, 

 together with the second axillary nervure (9-) and the inner margin, encloses an almost 

 semi-sagittate space; the first axillary nervure (9^) is strongly arched towards its extremity; 

 the second is essentially simple and very gently curved. Hind wings well developed, their 

 membrane devoid of a contracted longitudinal fold. Sette of moderate length in $ , very 

 long in d ; in dried examples the outer setas of 6 are divergent from the median setae 

 (wlien there are three) or divaricate (when the median is aborted). Eorceps-limbs inserted 

 at the sides of the terminal border of a short transverse laminar lobe prolonged from the 

 segment, which lamina is undeveloped in the $ , their proximal joint shorter than the 

 second, which is the longest joint. Nymph [Fentagenia (13) unknown] fossorial, with 

 tracheal branchiae inserted upon the sides of the respective segments in advance of the 

 unprolonged hinder lateral angles, and arched upwards over the back with the tips 

 turned posteriorly ; median lobe of tongue emarginate. Legs short and strong ; the fore 

 tibia and femm* pilose, tlie former compressed and obliquely truncate distally. 



HEXAGENIA, WalsL, 1863. 



Illustrations. Adult, PI. VII. 11 a-11 c (details) ; (whole figures,) see citations of 

 Guerin (1829-31), Gray (1832), and Eambur (1812), under II. hilineata ; also of Pict. 

 (1843-5) under II. variahilis. Nymph PI. XXIX. (whole figure and some details) and 

 PL LXIII. (other details) ; also Walsh, ' American Entomologist,' i. 6, woodcut (1868). 



Adult. — Pronotum in ? longer than broad, enlarged posteriorly, inflated medially, 

 slightly constricted at its anterior \ at the sides ; its arched and curved hinder border 

 rather prominent just in the middle, and somewhat rctuse when dried. Eore leg of 6 

 nearly as long as the body, the tibia about 1^, the tarsus about 1§ as long as the femur ; 

 ? fore femur but little shorter than the tibia, which is about as long as the tarsus. 

 Thoracic S2)iracles elongate, their lips straight-edged or nearly so, usually closed in dried 

 specimens ; but sometimes the anterior gapes narrowly in front ; its ujiper valve is much 

 the larger and is strongly concave within. Median seta extremely rudimentary in both 

 sexes ; outer setae generally upwards of 2J times as long as (in subimago about the 

 same length as) the body, in $ about § as long as it ; when magnified their surface is 

 minutely pubescent throughout, and their joinings are well defined. Terminal joints of 

 forceps-limbs small. Lobes of penis strongly hooked, and without apjiarent stimuli. 

 Abdominal segments of ? : — 1 and 2 very short, the first tlioracoid ; 3-6 rather short, 

 7-9 longer, 10 short ; 8 is the longest, and 9 about as long as 7. Anterior ocellus much 

 smaller than the others. Eyes of 6 suboval, curved, large, moderately distant from each 

 other above. Nymph in the construction of its tracheal branchiae, legs, and mouth- 

 parts very similar to Ephemera ; but the tusks of the mandibles are connivent, and the 

 frons is armed with a single obtuse median protuberance. Abdominal segments 1-7 

 brancliiferous ; the gills all double, those of the anterior segments arising each from the 

 upper surface of the pleural region of the segment in the hinder part of the same, but 

 the gills of the seventh segment issuing from it near the base ; the gill-roots armed (as 



