228 EEV. A. E. EATON ON EECENT EPHEMEEID,^ OR MAYFLIES. 



than the lacinia; the third joint subulate, as long as the second and longer than the 

 tirst ; lacinia nude on the crown, its terminal border beset with numerous curved 

 spines, its inner edge with a small isolated tuft of short hair in the middle. Lacinise of 

 maxillfB II. narrower than the lobes of the labium, which nearly resemble quadrants of 

 the longer segments of a short ellij)se ; pali^us chelate, the second joint being produced 

 distally on the inner side into a slender conical projection shorter than the terminal 

 joint. Median lobe of the tongue subquadrate, with the terminal corners rounded off, 

 and with the margin slightly mucronate iu the middle between them ; paraglossse 

 narrow, distally dilated and rounded off. Hind leg longer than the fore leg ; tarsus 

 (claw excluded) about 1| as long as the tibia. Pleurae of segments 6-9 of the abdomen 

 narrowly dilated oniscoidally ; their outer edges for some distance from the points 

 straight and oblique, and then rounded off. Setse all of one length, about ^ as long as 

 the body and plumosely pilose. Resident in swiftly flowing rivers on the underside of 

 stones, creeping slowly, but swimmiug with celerity. 



Type. B. obesa (in "^ Baelis), Say. 



Distribution. N. America. 



Etymology. Diminutive of Baitis, the classical name of the Guadalquivir, grecised. 



B.^TiscA OBESA, Say. Plate XXI. 37 (wings, legs, genitalia). 



Baelis obesa, Say, Journ. Acad. Nat. Sc. Pliilad. viii. 1.'3 (1839) ; Pict., Hist. Nat. Nevropt. ii. Epliem. 

 195 (1843-5) ; Walk., List of Ncuropt. Ins. iu Brit. Mus. part iii. 563 (1853) ; Lc Conte, Reprint of 

 Say's Works, ii. 412 (1859) ; Hag., Smitlison. Miscell. Coll. (1861) 45. 



Btetisca obesa, ! Walsh, Proc. Acad. Nat. Sc. Pliilad. (1862) 378 ; ! id., Proc. Ent. Soc. Philad. ii. 

 187 (1863); \id., ditto, iii. 200-G, fig. [uymph] (1864); ! Etu., Eut. Mo. Mag. v. 81) (1868); Packard, 

 (Juide to Study of Ins. ed. i. 595, fig. 576 [after Walsh] (1870) ; Etn., Trans. Ent. Soc. London 

 (1871), 101, pis. ii. 6 [wing; misdrawn] & v. 9 [details] ; Joly [translation of Walsh 1864], Bull. Soc. 

 d'Etud. Sc. Angers 1878-1879, pp. 157-173, figs. 1-3 [after Walsh] (1880); Vayssicre, Ann. d. Sc. 

 Nat. (6) Zool. xi. 4, 5, pi. i. 2 (1881) & xiii. 72-77, pis. vi. 56, is. 98-99 bis, & x. 99-103 (1882). 



Subimarfo (dried). — Wings dark sepia-grey with a narrow transparent colourless space 

 on each side of every cross vcinlet in the greater part of the disk, and with broader 

 coloitrless spaces elsewhere in the parts deticient in cross veinlets, viz. : — in the fore 

 wing a large clear band, ]}roadest in the hinder half of the wing, describing a curve from 

 the anal angle outwards to nearly the middle of the costa, and almost interrupted at the 

 fork of the prtebrachial (6) nervure ; also a large ii-regular blotch extending transversely 

 from the costa half across the sectorial intercalarv nervures : iu the hind wing the base 

 is pale, and the dark ground-coloiir, very sjmrsely varied with pellucid spots, extends to 

 .some depth along the terminal margin. Seta? light warm sepia-brown. — A sjiecimen 

 from Detroit, JVIich., has light yellowish-grey wings varied with dusky ; and in the fore 

 wing the lighter colour occupies almost the whole of the space posterior to the anal (8) 

 nervure ; also a broad patch, in continuity with that space, extending in proximity to 

 the wing-roots, and near the conjunction of the sector (4) and cubitus (5), to the radius 

 (3) ; also a band, likewise in continuity with the first-mentioned space, passing straight 

 across to the costa by the fork constituted by the union of the sector (4) with the 



