342 THE RIVER-SIDE NATURALIST. 



veinlets in the marginal and sub-marginal areas ; neuration 

 as a whole similar to that of species of Cloeon or Baetis. 

 There are only two British species. 



Centroptilum luteolum. Wings very faintly grey tinted, 

 sometimes very slightly tinted with the palest yellow ochre ; 

 setae greyish-white or cinereous ; turbinate eyes in male 

 imago, bright light-red ; simple eyes in female, greenish- 

 black or black. This insect is the same as Cloeon ochraceou 

 (Stephens), Cloeon translucida (Pictet). Eaton says it is 

 abundant in Great Britain, and reaches maturity in our 

 southern counties from April to November. No doubt 

 one of the Olive Duns, Centroptilum pennulatum, has in the 

 sub-imago state the wings a very little greyer than C. luteo- 

 lum; distinguishable by its greater size. The male imago 

 has the turbinate eyes of light cadmium orange, lower eyes 

 olive-grey or black ; those of the female imago olive-grey 

 or greenish-black. According to Eaton, it is common in 

 trout-streams from August to October. 



Eaton says : " Among miscellaneous representatives of 

 the genera, adult, and in good condition, Cloeon is easily 

 distinguished by the absence of hind-wings ; Baetis by 

 hind-wings broad and obtuse, with scarcely a cross veinlet 

 at all ; Centroptilum by the extreme narrowness of its 

 very small wings, and usually by the slenderness of their 

 costal projection. But to discriminate from Cloeon defec- 

 tive specimens of other genera deprived accidentally of 

 their hind-wings is a task attended with insurmountable 

 difficulty." 



In Cloeon the turbinated large eyes, with scarcely 

 any space between them, appear to be one of the chief 

 characteristics of this genus. The insects themselves are 

 also, as a rule, of very delicate structure, and of pale- 

 yellow or ochreous tint. 



The rudiment of a third seta can often be observed on 

 examination with a high-power lens. 



Stephens says that Baetis can be distinguished from 

 Cloeon, in the shape of the wings those of Baetis being 

 long and narrow and somewhat pointed ; those of Cloeon 

 rounded at the apex. 



