Devonian Insects to Later and Existing Types. 259 



what complicated : some of the wings, as PlatepJiemera and 

 GerepTiemera^ are reticulated ; the others possess only trans- 

 verse cross veins, more or less distinct and direct. No two 

 wings can be referred to the same family, unless Dyscritus 

 belongs with Homothetus — a point which cannot be determined, 

 from the great imperfection of the former. This compels us 

 to admit the strong probability of an abundant insect-fauna 

 at that epoch. Although many Palaiozoic localities can boast 

 a greater diversity of insect types if we look upon their general 

 structure as developed in after ages, not one in the world has 

 produced wings exhibiting in themselves a wider diversity of 

 neuration ; for the neuration of the Palaeodictyoptera is not 

 more essentially distinct from that of the Palajoblattarise or of 

 the ancient Termitina than that of Platephemera or Ger ephe- 

 mera on the one hand is from that of Homothetus or Xenoneura 

 on the other. Unconsciously, perhaps, we allow our knowledge 

 of existing types and their past history to modify our appre- 

 ciation of distinctions between ancient forms. For while we 

 can plainly see in the Palaioblattarige the progenitors of living 

 insects of one order, and in other ancient types the ancestors 

 of living representatives of another order, were we unfamiliar 

 with the divergence of these orders in modern times, we 

 should not think of separating ordinarily their ancestors of 

 the Carboniferous epoch. It may easily be seen, then, how 

 it is possible to find in these Devonian insects (all Neuroptera 

 or neuropterous Paleeodictyoptera) a diversity of wing-struc- 

 ture greater than is found in the Carboniferous representatives 

 of the modern Neuroptera, Orthoptera, and Hemiptera. 



11. The Devonian insects also differ remarkably from all 

 ether known types^ ancient or m,odern ; and some of them 

 appear to he even more complicated than their nearest living 

 allies. With the exception of Platephemera, not one of them 

 can be referred to any family of insects previously known, 

 living or fossil ; and even Platephemera, as shown above, 

 differs strikingly from all other members of the family in 

 which it is placed, both in general neuration and in reticula- 

 tion, to a greater degree even than the most aberrant genera 

 of that family do from the normal type. Thi.s same genus is 

 also more complicated in wing-structure than its modern 

 allies ; the reticulation of the wing in certain structurally- 

 defined areas is polygonal and tolerably regular, instead of 

 being simply quadrate, while the intercalated veins are all 

 connected at their base, instead of being free. Xenoneura 

 also, as compared with modern Sialina, shows what should 

 perhaps be deemed a higher (or at least a later) type of struc- 

 ture, in the amalgamation of the externo-median and scapular 



19* 



