EEV. A. E. EATON ON RECENT EPHE.MEEID^ OR MAYFLIES. 5 



Nervures of the fore icing. First group. — The costa (1), the subcosta (2), and 

 radius (3), are strong simple nervures, nearly of the same length, and almost parallel 

 with one another. Close to the base of the wing they are all connected by the great 

 cross vein, and still nearer to the wing-roots the hinder two are again bound firmly 

 by another strong cross vein. In Fal'mgenia and some other genera the costa and 

 subcosta are liable to be folded back under the radius, so that this last appears to skirt 

 the edge of the membrane for a considerable distance. In Massoi/euria (PI. III. 3) 

 the subcosta is completely suppressed ; and in no case is the adventitious mediastinal 

 ever developed in the Ephemeridte. 



Second group.— T\\q sector (4) and cubitus (5), the praebrachial (6) and pobrachial (7), 

 are the main nervures of the second group. The sector and cubitus (excepting in genera 

 allied to Oligoneuria, where one or both of them are suppressed) unite l)efore the middle 

 of the wing, and their common trunk joins the prsebrachial towards its termination. 

 The sector is usually reckoned as a branch of the cubitus by entomologists ; but it 

 constitutes a separate nervure in the hind wings of many Ephemeridse. Excepting in 

 wings very scantily nerved, the interval between tlie sector and cubitus is supplied with 

 adventitious nervures, usually five in number, but sometimes three or sis. "When there 

 are five of them, the fifth from the sector is the longest, the third the shortest of all, and 

 the first is longer than the second. In Cloeon and some other genera cross veinlets 

 afford the only communication between these and the main nervures ; but very fre- 

 quently most of them combine with the first or fourth, and that unites with the sector, 

 the fifth usually remaining alone. When the prsebrachial nervure is simple (excepting 

 in allies of Oligoneuria) two adventitious nervvires are always interposed between it and 

 the pobrachial nervure (PL XVI. & XVII.) ; when it is forked, its fork contains a single 

 adventitious nervure, and its hinder branch is followed by the pobrachial nervure imme- 

 diately Avithout the interpolation of any nervure whatever. The hinder branch of a 

 forked prsebrachial nervure is therefore evidently homologous with the second adven- 

 titious nervure, and should be accounted a false branch accordingly. The fork is ex- 

 tremely deep in (kmipsurus and Folymitarcys (PI. V. & VI.). 



The pobrachial nervure, somewhat deserted by its fellows, is essentially a simple nervure, 

 any branches which it may appear to have being (like those of the priebrachial) virtually 

 adventitious nervures introduced between it and the anal nervure. Because in this 

 as in the last instance referred to, when the pobrachial nervure is obviously simple 

 (PI. XVI. & XVII.), two adventitious nervures intervene between it and the anal 

 nervure (8), which sometimes annex themselves to the latter (PI. l.ll),\c); and when 

 the second of them simulates a branch of the pobrachial, the fork thus formed contains 

 a single adventitious nervure within it, and is follo^ved immediately by the anal. 

 Sometimes each of them unites with the nervure to which it is nearest (PL V. 8«); 

 in short, the combinations into which they enter with themselves and the adjoining 

 nervures are almost as many as are possible. In Palingenia lonylcauda (PL I. 1 a), pro- 

 vision seems to be made for the origination of several other adventitious nervures. 



Third G^-owj).— The anal (8) and the axillary' nervures (9', 9% &c.) complete the series 

 of main nervures in the disk of the wing. The former, as a rule, subtends the anal 



