﻿132 [November, 



Genus Centroptilum,* n. g. 



Sp. typ. O. luteolum, Mul. 



Syn. Ephemera, p., Mul., 1776. 

 Cloeon, p., Ste., 1835-6 ; Cloe, p., Burm., 1839. 

 Baetis (Leach), section A. Etn., 1868. 



Diagnosis. — Nymph agile, with seven simple pairs of undivided branchial 

 plates. Upper maxillary palpus slender, rather long, 4-jointed, with the first joint 

 the shortest, the second long and equal in length to the other two taken together, 

 which are sub-equal to each other. 



The sub-imago assumes the same posture as Baetis when reposing. 



Imago similar to Cloeon ; but with four wings. Hind-wing very narrow, with 

 a long costal process, and two simple longitudinal veins. 



Distribution. — The Palsearctic and Nearctic regions. Two Euro- 

 pean species are described, one of which (0. luteolum) occurs also in the 

 Hudson's Bay Territory. Besides these, there are an English and a 

 Carinthian species known to me, undescribed. 



Unfortunately I cannot just now lay my hands upon either speci- 

 mens of the nymph or preparations of the mouth organs of C. luteolum ; 

 therefore I am unable to speak positively about the structure of the 

 labium and lower maxillae ; but, so far as I can recollect, these are more 

 like those of Baetis than of Cloeon. The lab rum is widely retuse, as in 

 Ephemerella. 



In Cloeon the palpi are two-jointed, with sub-equal joints : the 

 upper maxillary palpi are very slender, filiform, and rather longer than 

 their maxillae : the lower maxillary palpi are slightly depressed, and 

 somewhat expanded towards their oblique tips ; and their maxilla? are 

 a little longer, but no broader than the divisions of the labium. The 

 labrum is narrowly emarginate. 



In Baetis the palpi are likewise two-jointed, with joints sub-equal 

 to one another : the upper maxillary palpi are slender, of tolerably even 

 diameter throughout, and not so very long : the lower maxillary palpi 

 are depressed and broadly expanded towards their rounded tips, the 

 basal joints being sub-cylindrical and stout ; their maxillae are longer 

 and much broader than the somewhat subulate divisions of the labium. 

 The labrum is narrowly emarginate. Professor Pictet's figure of the 

 labium and lower maxillae with their palpi (Pict. Ephem., pi. xxxvi, 9) 

 is not accurate. 



The mandibles are much alike in all of these three. 



Ashbourne, Derbyshire. 



15th September, 1869. 



* Derivation.— (Gr.) Kentron, a spur, and ptilon, a wing; so named in allusion to the costal 

 process of the hind-wing. 



