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NEW YORK STATE MUSEUM 



or three filiform appendages which terminate the abdomen are 

 here called caudal setae. 



The tarsi are typically five-jointed in the adult, though one or 

 two basal joints show a marked tendency to fuse with the end 

 of the tibia, and the last joint bears two claws of vari- 

 able form (Fig.5) ; in the nymph the tarsus is one- 

 jointed and lx*ars a single claw (Plate 6, fig. 7 and S). 

 The mouth parts in the adult are atrophied and functionless, 

 while in the nymph they are highly developed. But one feature 

 of them needs mention here, however; that is the armature of the 

 mandible. By comparing pl.G, fig.4, and pl.S, fig.G, it will be seen 



Fig. 1 Venation of the wings of Siphlurus; lettering explained in text 



that each mandible bears on its inner side a broad more or less 

 corrugated molar surface, and at its antero-lateral angle several 

 variable canines. 1 



To the venation of the wings the student who aspires to an 

 acquaintance with mayflies would do well to pay special heed. 

 This is of chief importance because 1) the venation is perfectly 

 definite and easily observed; 2) it suffers least distortion in pre- 

 served specimens; 3) it remains the same through the different 

 developmental stages, and 4) the wings are better retained than 

 the other appendages, and progress is better in using a key if the 

 structures mentioned in it have not been lost. The main features 



1 Following the terminology of Vayssiere for these parts. Organisation 

 des larves des Ephemerines: Ann. Sci. Nat. (G) vol.13. 1882. 



