106 EEV. A. E. EATON ON RECENT EPHEMEEID^ OE MAYFLIES. 



black. Legs pitch-black ; fore tarsus scarcely paler ; hinder tibite and tarsi rufescent- 

 piceous, the latter somewhat darker than the former. Wings vitreous with a somewhat 

 talcose gloss ; fore wing tinged with blackish (or in the dried insect, with fuscous) in. 

 the marginal and submarginal areas ; neuration piceous, the costa somewhat testaceous 

 at the base ; cross veinlets numerous in the marginal area of the fore wing, numbering 

 about 6 before the bulla and 16 beyond it ; those in the pterostigmatic region anas- 

 tomose irregularly with one another. Length of body 10; wing 10; setae, <S im. 12, 

 subim. 9 & 12 mm. 



Hab. Widely distributed in Europe, ranging from Belgium and Heidelberg (M°Lach.), 

 Dresden (Herr C. Schiller), and Switzerland (Pict.), to southern Italy and Portugal. 

 The nymph inhabits gently flowing shallow water, and attains maturity in summer 

 and autumn. 



THRAULUS, Etn. 1881. 



Illu8tratio7is. Adult (details), PI. XII. 20, and XIII. 20*, 2, 3. Nijmph, PI. XXXV. 



Adult. — Hind wing strongly and obtusely angulated in front, the angle in normal 

 species more nearly right-angled than in Ghorulerpes, placed almost in the middle of the 

 fore margin, and followed directly by a well-defined sinus at the termination of the sub- 

 costa (2) ; marginal area oblong, truncate distally, and, after the great cross vein, of 

 nearly uniform width ; submarginal area trilateral, the radius (3) somewhat undulated 

 in the typical species, the angles adjacent to it very acute, that subtended by it rather 

 obtuse : in the marginal area, and in direct proximity to the salient angle, a single 

 strong cross veinlet (or two at the most) communicates between the costa and the sub- 

 costa ; in the submarginal area are 2 or 3 between the subcosta and the radius, seldom 

 followed by a few others between the radius and the fore margin. Cross veinlets in the 

 normal species numerous in the fore wing, excepting near the terminal and inner margins, 

 which have no isolated veinlets ; they are absent also from the marginal and sub- 

 marginal areas l)efore the bulla. The nervures of both wings in the typical species are 

 generally 'branchless at the terminal margin ; when any branchlets do occur, which is 

 bul; seldom, they are very -scanty, simple, and peculiar to the individual wing. [Devia- 

 tions from the normal type of neuration are described below in the paragraph following 

 the definition of the genus.] The anal-axillar interspace of the fore wing contains 

 2, 4, or 5 intercalary nervures, two of them long, the others short ; when there are 

 two only, they extend | of the distance towards the wing-roots, and communicate by few 

 cross veinlets with both of the nearest nervures ; when 4 are present, the two shorter are 

 placed as in Choroterjies, all communicate more or less both mutually and with the said 

 nervures by cross veinlets, and all terminate abruptly ; when there are 5, the fifth shares 

 with another the intersj)ace between the longest two. The orifice of the mesothoracic 

 spiracle has valves only and lacks the guard. Porceps-limbs of cf 3-jointed ; the proximal 

 joint much longer than the remainder, and more or less dilated towards the base ; the 

 dilatation gradual in normal species. Eorceps basis short, entire ; homologous ventral 

 lobe of ? obtusely rounded at its extremity. ., Caudal setce 3, subequal in. length to each 

 other, mutilated in the typical specimens. Ungues in every tarsus dissimilar each to the 



