EEV. A. E. EATON ON EECENT EPHEMERID.E OE MAYFLIES. 201 



squarely truucate. Gradation of tarsal joints : — fore tarsus 

 (J 3 and 2 subequal to 4, 1, 5, ? subim. 2, 1, 3, 4, 5 ; 

 hind tarsus ^ 2, 5, 1, 3, 4, ? subim. 2, 1, 5, 3, 4. 

 [PL XX. ?346] Metamonius. 



subequal to the 2nd joint. Tarsal claws mutually dissimilar. Costal dilatation 

 of the hind wing almost right-angled. In J abdomen the 

 ventral lobe of segment 9 is subtriangular with the vertex 

 retuse ; pleurse of segments 7-9 squarely truncate. Grada- 

 tion of tarsal joints : — fore tarsus ^ 2, S, 4^ Ij 5, $ 2, I, 3, 

 5, 4; hind tarsus <S and ? 2, I, 5, 3, 4.— [PI. XVIII. 

 ?34e] Ameletus. 



longer than the 2nd joint. Tarsal claws mutually alikcj narrow and hooked. 

 Costal dilatation of the hind wing obtuse. $ unknown. 

 Gradation of tarsal joints : — fore tarsus 1 equal to 2, 3, 4, 



5; hind tarsus 1, 2, 5 subequal to 3, 4 Dipteromimus. 



Tibiae of the hinder legs shorter than the tarsi. Proximal joint of the hind tarsus 



longer than the 2nd joint. Tarsal claws mutually 



aUke. Costal dilatation of the hind wing obtuse. In $ abdomen the ventral 

 lobe of segment 9 is very short, parabolic or obtusely trian- 

 gular ; pleurae of the segments 7-9 obtuse behind. Grada- 

 tion of tarsal joints : — fore tarsiis ^ 2 equal to 3 and sub- 

 equal to 4, 1, 5, ? 1, 2, 5, 3, 4 ; hind tarsus J" 1, 2, 3 sub- 

 equal to 5, 4, ? 1, 2 subequal to 5, 3, 4 Siphlurus. 



dissimilar. Costal dilatation of the hind wing very small and obtuse. In $ 

 abdomen the ventral segment 9 is lobeless ; pleurfe of 

 segments 1-6 truncate behind^ of 3-6 slightly dilated 

 posteriorly, those of 7-9 broadly dilated laterally and pro- 

 duced posteriorly each into a short acute tooth. Gradation 

 of tarsal joints : — fore tarsus (J 1, 2, 3, 4, 5, $ 1, 2 sub- 

 equal to 5, 3, 4; hind tai'sus ^J and ? 1, 5, 2, 3, 4 Oniscigaster. 



COLOBURUS, Etn. 1868. 

 Illustrations.— Adult (details) Pis. XVIII. & XIX. a-c. 



Adult. — Fore leg of d about as long as the body [when dried 1 nj as long] ; tarsus 



about as long as the tibia, and this about If as long as the femur ; diminishing sequence 



of tarsal joints 2, 3, 4, 5, 1, the first joint nearly ^ as long as the second. Fore leg of 



the typical S about -j^ as long as the body ; tarsus about f as long as the tibia, which 



s about IJ as long as the femur ; tarsal joints in lessening length rank 5, 2 subequal to 



J, 4, 1, the first joint about ^ as long as the second. In an undescribed N. American 



species [PL XVIII. 326] the ? tarsus is about y as long as the tibia, and this about If as 



ong as the femur. Hind tarsus of the typical d about -^ as long as the tibia, and this 



ibout 1-^ as long as the femur ; the first joint is abovit f as long as the second, but both 



if them are short. Ungues in every tarsus each unlike the other. Hind wings weU 



'eveloped, oblong-oval, with the dilatation of the marginal area acute in front, and -with 



datively scanty neiu*ation in the narrow axillar region. In the ? abdomen the relative 



jngths of the 2nd-9th dorsal segments may be formulated approximately thus : — 5, 8, 



SECOISn) SERIES. — ZOOLOGY, VOL. III. 27 



