204 EEV. A. E. EATON ON EECENT EPHEMEEID^ OE MAYFLIES. 



is roundly emarg'inate Avith acute points. Porceps-basis of d variously excavated or 

 excised according to the species ; forceps-limbs 3-jointed, with the proximal joint 

 gibbous or slightly enlarged at its extreme base, and longer than the remaining joints 

 combined. Penis of various form, without apparent stimuli. Median caudal seta 

 sometimes totally aborted, and sometimes extremely rudimentary in the same species ; 

 outer setae about twice as long as the body in both sexes. Oculi of d obsoletely asca- 

 laphoid, contiguous above ; their inner orbits concave. Vertex of $ head longer than 

 broad, very little broader in front than behind, with the occipital border only slightly 

 raised and projected little beyond the level of the posterior orbits of the eyes. Median 

 ocellus rather smaller than the others and isolated, occuj)ying a small shallow depression 

 in front of and below the anterior edge of the upper surface of the head. Pronotum of 

 ? somewhat narrowly reflexed upon the mesopleurse ; its posterior margin opposite the 

 interspace between the eyes is almost straight, but minutely emarginate in the middle, 

 and retires to form a shallow recess thereabouts. Nymph [generical identification 

 doubtful]. — Abdominal tracheal branchiae borne by segments 1-7, all obovate and single. 

 Antennae shorter than the head and pronotum, abou.t 14.-jointed at maturity. Stipes of 

 the mandibles unusually short ; endopodites absent ; fangs slender, two in number. 

 Lacinia of maxilla i. unusually short and broad, beset on the crown with numerous 

 slender curved pectinate spines [somewhat in the same manner as that of Thraulus is 

 crowned with a tuft of hair], and ciliated for some distance from the point along its 

 inner edge; palpus equal in length to the lacinia, its first joint nearly of the same length 

 as the second, and longer than the third joint. Laciuise of maxillae ii. somewhat falci- 

 form, much narrower than the lobes of the labium ; these are unusually broad, trilateral, 

 with the outer side saliently rounded off and the other sides nearly straight, and are 

 spinulose along their distal borders. Paraglossae roundly expanded distally, and longer 

 than the subrotund median lobe of the tongue. Abdominal pleurse narrowly dilated, 

 and with short acute points behind. Hind leg nearly of the same length as the fore 

 leg ; tarsus (claw excluded) about as long as the tibia. Setae subequal in length to one 

 another, and i as long as the body ; median seta plumose, the others ciliated on the 

 inner side ; their fringes taper towards the points. 



Type. Ch. ignotus (in % Baetis), Walker. 



Distribution. Continental Europe, in large rivers ; N. America ; Sumatra (undescribed 

 sp.). 



Etymology. -^eipoTovriTriQ, one that stretches out the hands, from the attitude of the 

 imago in repose. 



Synonymous with % Ba'etis (B), Walsh, 1862, and \\Isonychia, Etn., 1871. 



The nymphs referred here provisionally were sufficiently matured to show that the 

 tarsi of the imago are 5-jointed ; and so far as their wing-neuration could be ascertained, 

 there was nothing adverse to their being placed here. Length of body 9, setae 4'5 mm. 

 Five specimens collected by Mr. Hubbard at Trenton Falls, N. Y,, on 20th May, 1874 

 [the typical set], and one captured hj Lieut. Oarpeuter near Denver and Colorado 

 Springs in the Foot HiUs, Color., in 1873 [Mus. Comp. Zool. Cambridge, Mass.], are the 

 materials studied. 



