282 Mr. A. E. Eaton on the Anatomy of Ccenis. 



whereas those of the typical species (if they are not 

 mucronate) seem to be bi-articulate . 



To conclude^ it will be seen that^ in its preparatory 

 states, Ccenis differs considerably from other Ephemeridoe 

 in their corresponding stages of development, so far at 

 least as we are at present acquainted with them. But at 

 the same time, it sufficiently resembles the young of 

 Ephemera and Palingenia, in those points wherein it differs 

 from Baetis, Leach ((7/oe, Burm., Pict. p.) to authorise the 

 opinion of those who associate it with the former two genera 

 rather than with the last. In Baetis, although the wings of 

 the adult insect are not very unlike those of Ccenis, the 

 labium and its palpi are very differently constructed, the 

 branchial lamellae are entire, and in its subaqueous stages 

 the insect climbs the water weeds, or runs over the sur- 

 face of the bottom, and swims with a quick dashing 

 motion. These peculiarities of Baetis contrast with the 

 burrowing habits, the production of the edges of the 

 respiratory plates into fringing processes which contain 

 subdivisions of the branchial tracheee, etc., of Ccenis, — 

 particulars wherein it is approximated to Palingenia and 

 Ephemera. With these two genera, Ccenis is moreover 

 connected by Oligoneuria, Pict., which approaches, in its 

 adult condition, Polymitarcys and Campsurus (genera 

 which I have dismembered from Palingenia, Burm., Pict., 

 typified respectively by P. virgo, 01., and C. latipennis,' 

 Walk.), as may be shown by a comparison of their heads, 

 forceps, and other organs, and the duration of their sub- 

 imago states. On the other hand, Ccenis is also related 

 to Leptophlehia,, Westw., and Ephemerella, Walsh. Thus 

 a great similarity exists between its labium, labial palpi, 

 legs, and abdominal segments, and the corresponding 

 parts of the last-named genus, to whose gills the protect- 

 ing gills of Ccenis admit a tolerably close comparison. 

 Further, the branchial lamellae of Leptoplilehia, and its 

 forceps, are constructed much in the same way as the 

 membranous gills of Ccenis, and the forceps of Oligoneuria. 

 Seeing, then, that Leptophlehia and Ephemerella are in 

 some degree connected with Epliet]i.era by Potamanthus, 

 (restricted, type P. luicus, L., Pict.) , and that they are also 

 related to Ccenis and Oligoneuria, and that these in tlieir 

 turn are allied to Canipsivnis and Polymitarcys, I am inclined 

 to consider Ccenis and Oligoneuria collateral with the group 

 of genera to which Ephemera and Campsurus belong. 



