EEV. A. E. EATON ON EECENT EPHEMERID.E OE MATELIES. 229 



second intercalary in advance of the cubitus (5). Setae, forceps, and legs dull light 

 yellowish ; the ungues burnt-umber brown. 



Imago {dried), ? . — Notuni rather dark burnt-umber-, or intense warm sepia-brown. 

 Abdomen above dark burnt-umber, varied with lighter, and modified at the sides near 

 the base with blue-purplish grey ; venter reddish white, with a longitudinal fuscous 

 line in the middle of the penultimate segment. Setye pubescent, yellowish white, with 

 rufescent joinings. " Intermediate setae ferruginous " [Walsh]. Forceps yellowish white. 

 Tore femur light amber-yellow, modified with brown-ochre towards the tip ; tibia and 

 tarsus brown-ochreous, with pitch-brown ungues ; in transmitted light the light amber 

 predominates. Hinder legs lighter than the fore legs; the tibia and tarsi yellowish 

 white. Wings vitreous ; longitudinal neuration of the fore wing translucent light 

 brownish, excepting the bases of the costa, radius, and axillary nervvires, which ai-e 

 pitch-brown ; the marginal area of this wing contains about 10 very faint cross 

 veinlets before the bulla, and 17 beyond it. 



$ . Very similar. Length of body 6-8; wing 9-12 ; setse, 6 2 im. 6-7, subim. 6 3-5, 

 ? 4-5 mm. 



Hab. North America ; Illinois (Walsh) ; Indiana (Say) ; Detroit, Mich. (Mus. Comp. 

 Zool. Cambridge, Mass.) ; California (M'Lach. Mus.). 



The Michigan subimago above described probably agrees with the precocious 6 

 referred to by A^'alsh at tlie end of his description in 1862. 



Provisional Second Series of Group III. of the Genera of the EphemeridcB. 



Adult nriknown. Nymph. — Palpi of both pairs of the maxillse multiarticulate ; that 

 of maxilla i. far shorter than tlie lacinia ; that of maxilla ii. much longer than the 

 lacinia, flagelliform and geniculated. Abdominal tracheal branchiae diversiform, borne 

 by segments 1-7 ; the foremost formed each of a narrow membranous lamina with long 

 fringes ; those of the second segment are composed of a rounded pergamentose lamina 

 with a fascicle of fibrils annexe:! to its base ; those of the remaining segments have been 

 lost in the unique specimen. 



Section 12 of the Genera. — Tj^q nameless. Separated provisionally from Section 13 

 [see page 22]. 



Genus and Species undetermined. 



Illustrations. Nymph, PI. LIII. (slough and details). 



I^ ymph-slough. — Antennae shorter than the head, multiarticulate and subulate, with 

 the first two joints longer and much stouter than the remainder. Labrum transverse 

 and emarginate. Mandibles virtually symmetrical, each with two fang-like lobes pro- 

 jecting inwards nearly at right angles with it almost in the middle ; of these the lowest, 

 representing the molar portion of the crown, ends in a short sharp tooth dominating a 

 small excision; the intermediate fang is bifid, with acute unequal points; the extremity 

 of the mandible, narrowed cuneately from the lobes to the points, is slightly incurved 

 and trifid, with the median tooth the longest. Maxilla i. broad ; lacinia short, termi- 



SECOND SERIES. — ZOOLOGY, VOL. III. 31 



