144 ME. EOBEET MCLACHLAN Olf 



two at the base are much stouter than the others ; they gradually 

 diminish in stoutness from base to apex, the apical joint being 

 subacute. (As these organs are wanting in the more mature 

 individual, it is impossible to say if the number of joints varies 

 according to age.) The thoracic lobes (whence the wings eventu- 

 ally proceed) only partially cover the sides of the second abdo- 

 minal segment. In other respects this individual does not differ 

 structurally from that above described, only that (supposing it 

 to be also a male) there are no indications of the rudimentary 

 appendages &c. 



This remarkable insect would appear to be common at Christ- 

 church ; for Mr. Wakefield says the cast subimaginal skins are no 

 rarities there, sticking on walls, windows, &c. ; and he modestly 

 accords the credit of its original discovery to his fellow townsman 

 Mr. Fereday, who some years since sent an individual intended 

 for me to this country, but which, by an accident, never came 

 under my notice. 



The Eev. A. E. Eaton (the author of the elaborate ' Monograph 

 on the Ephemeridee ' in the Transactions of the Entomological 

 Society of London, 1871, Part i.) remarks that the structure of 

 the aquatic conditions shows that the creatures are of active 

 habits, swimming freely among water-plants, &c. and not semi- 

 fossorial, as is the case with some members of the family. 

 He thinks the genus related to Siphlurus (which has an 

 indication of lateral expansions of the abdominal segments), 

 and through it distantly to Cloeon, but in the earlier states 

 rather than in the imago ; for Cloeon has double eyes in the 

 male. "With regard to my idea of there being a second smaEer 

 branchial plate under the large upper one, he rather inclines to 

 the belief that it is only an illusory appearance caused by infla- 

 tion with the spirits ; but to my eyes the appearance became more 

 marked in a plate I had detached, and which became dry from 

 evaporation. I tender my warmest thanks to Mr. Eaton for 

 information as to probable habits and affinities, which his critical 

 knowledge of the group renders additionally valuable. 



The great lateral expansion of the margins of the abdominal 

 segments is without a parallel in any known perfect insect of the 

 group. In the aquatic conditions there are occasional indications 

 of it, especially in the extraordinary Bcetisca olesa of Say, a 

 North- American species, the nymph of which has been described 

 by the late B. D. Walsh (from specimens found in Illinois). 



