146 Mr. A. E. Eaton on some Species 



contained fluid into the intestine, over which ramify branches of 

 the tracheal trunks. The distribution of these trachese varies, 

 possibly according to the age of the insect; yet the branches 

 (in a Cloeon) which are given off from the trunks in the seventh 

 and eighth segments (Dr. Schaum's method of reckoning) are 

 larger than those in the other segments, especially in young pupae. 



The genus Cloeon, as limited by M. Pictet, whom Dr. Hagen 

 follows, may be at once divided into two groups, which in reality 

 are genera, although not recognized as such hitherto. As it is 

 therefore necessary to propose a name for one of them, I will 

 suggest that Cloeopsis be given to C diptera, L., on account of 

 a variety of the male resembling in colour Cloe or Cloeon Rho- 

 dani, Pict. 



Cloeopsis, nov. gen. 



Comprises one widely distributed species, C. diptera, L. 



Gen. Char. — Pupa with six pairs of double branchial plates 

 and one pair of single ones. Imago dipterous, with two anal 

 setse, the third abortive. 



In this species the larger division of the double branchial plates 

 of the pupa is nearly circular; the smaller is indicated by the 

 dotted line in the figure. The single plates are also 

 circular. It may perhaps be unnecessary to mention 

 that, although Dr. Hagen has included it in his dia- 

 gnosis of the pupa, the possession of black wing- 

 cases is indicative of state, and is not a special cha- 

 racter; in Cloeon Rhodani, and some other species 

 also, these organs become black shortly before the final change 

 of the pupa. Dr. Hagen, too, attaches great importance to the 

 markings or absence of colour in the setae of the imago, as well 

 as to the colour of the turban of the male. But there is scarcely 

 any colour-character which, when fully tested, is not found to 

 vary more or less in the species of this family. Specimens of 

 this insect from Cambridge and Huntingdon often have the 

 turban dull greenish yellow (like the legs of C. Rhodani subim.), 

 instead of reddish brown (eyes of house-fly) ; and in the same 

 localities the female generally has colourless wings, like the male. 

 The setse are frequently not annulated. 



Cloeon (as restricted). 



Gen. Char.— Pupa with seven pairs of single //^v^^ 

 branchial plates. Imago with four wings and f:^^ 

 two anal setse; third seta abortive. pi^teofpupa(sp??). 



In this genus the form of the rudimentary hind wings is very 



useful in determining the species, as it does not vary to any 



