2 EEV. A. E. EATON ON EECENT EPHEMERID.i: OR MATELIES. 



kindred species are often so nearly alike in colour that terms of precision are indis- 

 pensable in describing the differences between them. When it was settled that the 

 work should be written in its present form, the exigencies of the case were met 

 by having recourse to a trade-colour pattern-book, as a standard of reference, sold by 

 one of the principal artists' colour merchants in London. The samples display three or 

 four gradations of each colour, — intense, medium, light, and sometimes very light. In 

 my descriptions, colours of medium gradation are usually quoted without any qualifying 

 adjective ; but in blacks, only the intense gradation is termed black, the medium being 

 designated greyish black, or blackish. The light gradation in blacks and browns, or 

 sometimes the lighter and lightest in a quadruple series of the latter, are referred to as 

 greys of such and such a tint. Very light gradations of red, orange, yellow, green, blue, 

 &c. are denoted as " extremely light," " the lightest possible tint," or " whitish," 

 according to circumstances. 



During the interval which will elapse between the issue of the successive parts of this 

 monograph, opportunities will doubtless occur of supplementing the illustrations of 

 species. A list of all additional tigures not cited in the text relating to the species 

 represented by them will therefore be given in the final part ; and references to them 

 can be made addenda. 



Structure of the Ephemerid^e in General. — Adult. 



The Ephemeridaj are insects with a long, soft, ten-jointed, sessile abdomen, furnished at 

 its hinder extremity with either two or three many-jointed setaceous or filiform tails 

 (caudal setae), and whose body is smooth and glabrous. 



Head free, with atrophied mouth-organs, carinated epistoma, short subulate antennae, 

 composed of two short stout joints succeeded by a slender many-jointed setaceous awn, 

 three ocelli, and large oculi (compound eyes). 



Thorax robust ; mesothorax predominant ; sternum well developed ; fore wings 

 ample, erect or spreading in repose, plaited lengthwise but not folded up (excepting 

 when a female happens to be ovipositing under water, and then they are reclinate and 

 compactly plicate like a closed fan) ; legs slender, femora strong, the fore coxre some- 

 what distant from, the others. 



Abdomen armed with a pair of claspers (forceps), in the male placed ventrally at the 

 extremity of the penultimate segment ; the vasa deferentia have each of them a separate 

 iutromittent organ situated at the ventral joining of the ninth and tenth segments. In 

 the female the oviducts terminate separately in the joining of the seventh and eighth 

 segments ; there is no real ovipositor, but in some genera (e. g. Reptagenia) the apex of 

 the seventh segment is produced beneath into a short rounded flap, and in one 

 {Hagcmdus) this projection takes the form of a spout. In many genera there is a similar 

 extension uf the ninth segment in one or in both of the sexes. Alimentary canal capa- 

 cious, straight, filled with gas, and apparently destitute of salivary glands ; malpighian 

 tubules in most instances indefinitely numerous, capillary, very long and entangled ; but 

 in Prosoplstoma shorter, stouter in proportion, fewer in number, and combined into one 

 common duct on each side. Tracheae filameutose or capillary, not sacculated, furnished 



