FOSSIL COCKROACHES OP NORTH AMERICA. 149 



characterized hy a remarkable openness of the ueuration in the middle of the wings, and by 

 their frequent exceptional length and slenderness. In Ohio this type comprises nearly three- 

 fourths of the species in these two genera, and in West Virginia about a fourth of the species. 

 The only occurrence of a similar form in Europe is in a species from the lower Dyas of 

 Weissig, Saxony, Etoblattina elongata. 



Now, although these localities are not far removed either geologically or geographically, 

 one in extreme eastern Ohio, the other in extreme northern West Virginia, not a single 

 species has been found common to the two. Almost without exception the same may be 

 said of any two localities in North America, even at the same geological horizon ; and not 

 a single fossil American cockroach is identical with any European form. 



This leads one to believe that when the insect fauna of our rocks is better known, these 

 insects may prove a better or rather a more delicate test of the relative age of rocks in the 

 Carboniferous series than the plants, many of which certainly range through an enormous 

 period of time, while insects have proved more sensitive to change. 



To take a first step toward publishing evidence which may be used hereafter in such 

 discriminations, I have made careful inquiry as to the exact locality at which each specimen 

 was obtained and have taluilated the species by horizons, based on that information. From 

 that tabulation I have prepared the next table, showing the geological distribution both in 

 Europe and America, of all the genera of Palaeozoic cockroaches known. In this I have 

 roughly separated the species from the true productive Coal-measures (i. e., above the " Mill- 

 stone Grit" and below the "Barren Coal measures") into an upper and a lower series, 

 endeavouring as far as possible to make the lower series correspond to the Coals A to C of 

 the Pennsylvania series. The Palaeozoic European species have been separated by the aid of 

 tables already published by Dr. H. B. Geinitz and Herr Kliver. The later European genera 

 are not considered. A. America ; E-Europe. (See page 150.) 



This table shows the genera so far known to exist on both continents at each successive 

 horizon. It further shows that Etoblattina and Gerablattina were of the first importance 

 in Europe as in America, Etoblattina in fact containing on either continent just about one- 

 half of the species of cockroaches found on that continent. It also brings out conspicuously 

 the fact that no Mylacridse have yet been described from Europe. 



The table again introduces us for the first time to our Mesozoic cockroaches and shows 

 the vertical range and the systematic grouping of the half dozen genera occurring in a 

 single pit in the Trias of South Park, Colorado. Later Mesozoic forms are as yet unknown 

 in America, but in Europe they are very abundant and we already know about seventy 

 species of ten genera. Without exception they are ISTeoblattarise, i. e., they differ from 

 Palaeozoic forms as do the existing types. But in the Triassic fauna of Colorado we have an 

 assemblage of forms of an intermediate character. Here are Palseoblattarite and Neoblattarias 

 side by side. The larger proportion are Palœoblattariœ, but of these all are specilically and 

 most of them generieally distinct from I'aheozoic species and all rank high among Blatti- 

 narife. We find, first, forms in whieli the fore wings are diaphanous, with distinct medias- 

 tinal and scapular veins, and the anal veinlets run to the border of the wing (Spiloblattina, 

 Poroblattina) ; next, those having a little opacity of the fore wings, with blended medias- 

 tinal and scapular, and the anal veins as before (certain species of Neorthroblattina) ; then 

 those with still greater opacity, with the same structural features (other species of Xeor- 

 throblattina) ; next, those having a coriaceous or leathery structure, blended mediastinal 



