1888.] 29 



A CONCISE GENEKICAL SYNOPSIS, WITH AN ANNOTATED LIST, 

 OE THE SPECIES OE BEITISH EPHEMERIDM. 



BY REY. A. E. EATON, M.A., F.E.S. 



{Concluded from p. 12). 



The species of Baetis are difficult to separate from one another 

 by concise diagnosis without illustrations, if indeed it be at all possi- 

 ble to distinguish thcin by this method satisfactorily. 



A. — Second nervure of the hind-wing simple ,B. 



„ „ „ „ „ forked Species 22 and 23. 



B. — Turbinate <J eyes yellow Species 15. 



„ „ „ reddish-brown Species 16 — 21. 



15. Baetis binoculatus, Linne : Mon., Ill, pi. ii, 9, and v, 16, 16a 



[adult details] ; Eevis., 158, pi. xvi, 295 [adult details] (1885). 

 Terminal joint of $ forceps limb comparatively largo, ovoid ; penultimate joint 

 slightly dilated near the middle. Apt to be mixed with Cloeon rufulum, and even 

 Centroptilwm luteolum in collections. 



May to October. Rivers. Common. 



16. Baetis scambus, Eaton: Mon., 112, pi. v, 17, 17a ; Eevis., 160, pi. 



lxiv, 9 [adult details] (1885 and 1887). 

 Hard to separate when dried from the preceding species. Eorceps more slender, 

 with the terminal joint relatively longer and less obtuse, and with the bases of the 

 limbs rather closer together. 



Summer and autumn. Streams. 



17. Baetis vernus, Curtis : Eevis., 161, pi. xvi, 29a 7 [forceps] (1884), = 



B. phcBops, Cat., p. 9 ; Mon., 115, pi. v, 21, 21a [adult details]. 

 Differs from JB. rlwdani in having a relatively larger and oval terminal joint to 

 the forceps limb ; in having a very slight denticulation at the interior extremity of 

 the second joint ; and in having a well-marked callus at the corresponding part of 

 the basal joint. 



Early summer and autumn. 



18. Baetis rhodani, Pictet : Mon., 114, pi. v, 20, 20a [adult details] ; 



Eevis., 161, pi, xvi, 29c, and lxiv, 12 [adult details], and pi. xliv 

 [nymph] (1884,5, and 7). 

 Forceps slender ; terminal joint small, sub-globular. 

 April to October, and mild weather in winter. 



19. Baetis atrebatinus, Eaton : Mon., 113, pi. v, 19, 19a [adult details] ; 



Eevis., 164, pi. lxiv, 15 [forceps] (1885 and 1887). 

 Differs from B. rlwdani in the hind-wing lacking the costal mucro ; forceps 



