EEV. A. E. EATON ON EECENT EPHEMERID.E OR MAYFLIES. 157 



often somewhat curved, and usually much the longest ; fourth joint commonly suh- 

 globular or oval and much the shortest, seldom elongate-oval and as long as the third. 

 The interspace between the basal joints of the forceps-limbs varies in relative width with 

 the species. Lobes of the penis without apparent stimuli. The intermediate segments 

 of the S abdomen are mutually subequal in length. Caudal setre in c? im. 2-2i, in 

 2 im. li-2i, in S subim. IJ-ly, in $ subira. -I-lf as long as the body. Fore tarsus 

 of d very nearly of equal length with the tibia, Avliich is about 1^ as long as the femur ; 

 its joints in diminishing succession rank 2, 3, 4, 5, 1 : fore tarsus of 2 about f as long as 

 the tibia, which is jast as long as the femur ; its joints rank 2, 5, 3, 1, 4. Hind tarsi of 

 <S about § as long as the tibia; the joints, shorter than in the $ , rank ], 4, 2, 3. 

 Nymph. — Abdominal tracheal branchioe all somewhat alike in form, each obtusely ovate 

 or obovate and traversed lengthw ise by a pinnately branched, irregularly subdivided 

 trachea. Antennsc about as long as the head and thorax together. Outer caudal seta) 

 about f as long as the body ; median seta commonly f as long as it, but in some s[)ecies 

 (e. g. _B. melanoHyx) of shorter proportions ; the fringes narrowed acuminately to the 

 extremities of the setre. Each mandible terminates in a slightly prolonged, compressed, 

 and obliquely abrupt lobe, eroso-denticulate at its termination ; endopodite absent. 

 Palpus of maxilla i. as long as the lacinio, 3-jointed ; the terminal joint slender and 

 about as long as the other two together : the lacinia armed with compressed teeth at 

 the point, that are preceded by a scries of setula) on the inner edge, arranged evenly and 

 gradually increasing in length aw"ay from the teeth, so as to constitute an acute oblique- 

 pointed ilatteued beard. Lacinia? of maxillteii. narrow and cultriform, broader than the 

 subulate lobes of the labium ; proximal joint of the palpus about as long as the remainder, 

 which are compressed and combined into a clavate piece rounded at the tip and slightly 

 indented on the inner side just before the tip, the terminal joint being subrotund and 

 somewhat imperfectly delimited by suture from the penultimate joint. Tongue, as a 

 whole, cuneate, with the narrower extremity truncate ; the median lobe narrower than 

 the paraglossce and bluntly mucronate. Hind tarsus, claw excluded, about f as long as 

 the tibia ; the leg altogether about as long as the fore leg. Resident in running water 

 and lakes ; two brooded in temperate regions. 



Type. JB. binoctilatns (in Ephemera), Linn. 



Distribntion.. Europe, including Egypt and Greenland; Northern and Central 

 America, the Argentine Republic, and perhaps Chili; Asia; Indo-Malay region and 

 Australia. 



Etymology doubtful; probably a misreading of Bsetis, the classical name of the 

 Guadalquivir. 



Synonymous with Brachyphlehla, "Westwood (18-iO). At p. 20 ante reference is made 

 to the identity with Bactis of the nymphs partly figured in detail l)y M. Vayssiere (1882) 

 under the name % Centroptilmn; and also to the probability of those quoted by him as 

 X Gloeoii being only junior grades of the same. The difference in form of the lamina) of 

 their tracheal branchia?, judging from the description, is such as might readily be pro- 

 duced by the alcoholic solution in which the specimens were preserved. Distention of 

 these laminte by endosmosis, to a large or small extent, is an accident of common 



