Devonian Insects to Later and Existing Ttjpes. 257 



its immediate allies. There are other Palseodictyoptera in the 

 Carboniferous period with more complicated neuration than 

 Dictyoneura ; but these three Devonian insects apparently 

 surpass them, as well as very nearly all other Carboniferous 

 insects. Furtliermore, 



7. With the exception of the general statement under the 

 fifth head, they hear little special relation to Carhoniferous 

 forms^ having a distinct fades of their own. This is very 

 striking ; it would certainly not be possible to collect six wings 

 in one locality in the Carboniferous rocks which would not 

 prove, by their affinity with those already known, the Carbo- 

 niferous age of the deposit. Yet we find in this Devonian 

 locality not a single one of Paloeoblattarife, or any thing- 

 resembling them ; and more than half the known insects of 

 the Carboniferous period belong to that type. The next most 

 prevailing Carboniferous type is Dictyoneura and its near 

 allies, with their reticulated wings. Gerephemera only of all 

 the Devonian insects shows any real and close affinity with 

 them ; and even here the details of the wing-structure, as 

 shown above, are very diffisrent. The apical half of the wing 

 of Xenoneura (as I have supposed it to be formed) also bears 

 a striking resemblance to the Dictyoneuran wing; but the 

 base (which is preserved, and where the more important 

 features lie) is totally dilferent. The only other wing which 

 shows particular resemblance to any Carboniferous form (we 

 must omit Dyscritus from this consideration, as being too im- 

 perfect to be of any value) is Platephemera, where we find a 

 certain general resemblance to Ephemerites Rilckerti^ Gein., 

 and Acridites priscus, Andr. ; but this is simply in the form of 

 the wing and the general course of the nervules ; when we 

 examine the details of the neuration more closely, we find it 

 altogether different, and the reticulation of the wing polygo- 

 nal, and not quadrate as in the Carboniferous types *. In 

 this respect, indeed, Platephemera differs not only from all 

 modern Ephemeridee, but also from those of other geological 

 periods f. Another prevailing Carboniferous type, the Ter- 

 mitina, is altogether absent from the Devonian. Half a dozen 

 wings, therefore, from rocks known to be either Devonian or 

 Carboniferous would probably establish their age. 



* Dr. H. B. Geinitz has kindly reexamined Ephemeiites Riickerti at 

 my request, and states that the reticulation is in general tetragonal, but 

 that at the extreme outer margin the cells appear in a few places to be 

 elliptical five- or six-sided. 



t The Dictyoneur<B and their allies, as may be inferred, are considered 

 as belonging to the PalaBodictyoptera, although their ephemeridan affini- 

 ties are not disregarded. 



Ann. & Mag. N. Hist. Ser. 5. Vol. vii. 19 



