REV. A. E. EATON ON RECENT EPHEJIERID.E OR MAYFLIES. 141 



slightly dimmed with very light sepia-greyish ; neuratiou pitch-brown. Fore legs and 

 hinder femora greyish black; hinder tibiie and tarsi greyish white. Setae dull whitish. 

 Length of body (shrunken) 4 ; Aving 8 ; setae about 8 mm. 



Hub. Cordova, Argentine Eepublic (Mus. Comp. Zool. Cambridge, Mass.). 



C.ENIS, Steph. 1835. 



Illustrations. Adult (details), PL XV. 26 a, h ; (whole figures) Steph. (1835) under 

 C. halterata (macrura), and Pictet under C. haltcrata {grisea) and lactella (J lactea). 

 Nymph, PL XLII. 



Adult. — Hind wings absent. Caudal set?e 3, mutually subequal, the median being 

 sometimes a little longer or shorter than the others, which in 3 im. are from 3| to 5 or 

 6 times as long as the body, and in 2 about f as long as it ; in neither sex are the setae 

 of the subimago much more than ^ as long as the body, and therefore their joints in the 

 cf undergo excessive elongation during the last moult ; in e im. they are uniformly 

 glabrous, but in ? im. the seta3 are pubescent from near their roots to the tips. Cross 

 veinlets almost exclusively uniserial, remote from the margin and absent from the mar- 

 ginal area ; terminal and inner margins of the wings devoid of rudimentary veinlets ; no 

 branchlets to the longitudinal nervures. The anal-axillar interspace contains two long 

 intercalar nervures of nearly equal length, either of which is met by the other just before 

 annexing itself to the anal (8) nervure near the series of cross veinlets, and at a distance 

 from the inner margin of about f of the interval between its own extremity and the 

 costa ; the fork formed by their conjunction is narrow and deep, and the curvature of its 

 sides nearly uniform. The recurrent membrane of the wing-roots does not extend beyond 

 the scutellum. Homologue of the forceps-basis undeveloped in ? . Pleura3 prolonged 

 posteriorly in segments 7, 8, and 9 of the abdomen into setaceous-acuminate or subulate 

 teeth. Forceps-basis entire ; forceps-limbs jointlcss and short ; penis exposed, undivided, 

 without apparent stimuli. Ungues of the hinder tarsi of 6 , and of all the tarsi of 2 , 

 each unlike the other ; those of the d fore tarsus alike, rotund. Fore tarsus of 6 , 

 exclusive of joint 1, about f as long as the tibia, which is about twice as long as the 

 femur ; its joints in diminishing order rank 2, 3 subequal to 4, 5 ; joint 1 is not distinctly 

 marked off from the basis. Fore tarsus of ? 4-jointed, about f as long as the tibia ; 

 this and the proximal joint of the former together are very little more than f as long as 

 the femur. Hind tarsus ? f as long as the extreme length of the tibia ; its joints rank 

 4 (the terminal), 1, and 3 subequal to 2. The theoretical first joint in these tarsi is 

 imdeveloped ; the femora are relatively broad. During quiescence the subimago stands 

 upon all its feet, with the caudal setaj laid together, and the wings usually widely 

 outspread, rarely erect. Nymph. — Body broadest at about the mesothorax, but not so 

 in a marked degree ; head a little narrower than the pronotum, varying slightly in contour 

 with the species. Pronotum transverse, its lateral borders sometimes dilated, and pro- 

 longed somewhat in front. Abdomen narrowed gradually in its hinder half, the anterior 

 segments difi'ering little from one another in breadth ; 1st ventral segment thoracoid, 

 2-5 shorter than the succeeding segments ; ventral segments 2-6 together about as long 

 as 7-10 together ; pleurte dilated, posteriorly acute or acuminate. Tracheal branchiaj 



SECOND SERIES. — ZOOLOGY, VOL. IIL 19 



