A certain amount of geological evidence may also be claimed in support of this view. A survey of the species of the two groups found up to the present time in America, published and unpublished, shows that all the _Mylacridæ_ are found below the Upper Carboniferous, while more than half the _Blattinariæ_ are found in or above it. This results largely from a recent and as yet unpublished discovery of _Blattinariæ_ in the Upper Coal Measures of Ohio and West Virginia, which in their general features are much nearer than previously discovered American Cockroaches to the European _Blattinariæ_, the latter of which come generally from Upper Carboniferous beds. The _Mylacridæ_ have therefore been found in America in strata generally regarded as older than those which in Europe have yielded Cockroaches, and this gives a sufficient explanation why no _Mylacridæ_ have yet been found in the Old World. In America one is mostly dealing with absolutely older forms, and they naturally give that continent a more old-fashioned look, when we regard the Carboniferous fauna as a whole. As already stated, a wing from the French Silurian (_Palæoblattina Douvillei_ Brongn.) has been claimed as a Cockroach, but without good reason, and to see a real old Cockroach one must look to America. Up to this point we have contrasted the palæozoic Cockroaches with the existing forms only, and finding such important distinctions between them, we naturally turn with some curiosity to the intermediate mesozoic and tertiary formations. Now, not only are the mesozoic species as numerous (actually, but not relatively) as the palæozoic, but a recent discovery of a Triassic fauna of considerable extent, in the elevated parks of Colorado, presents us with a series of intermediate forms between those peculiar to the Coal Measures and those characteristic of the later mesozoic rocks. Excluding, however, for a moment this Triassic fauna, we may say of the later mesozoic species that they are _Neoblattariæ_, not _Palæoblattariæ_, though they still show some lingering characteristics of their ancestry. Thus the front wings are in general of a less dense texture than in modern times, but without the perfect diaphaneity of the palæozoic species; in some the anal veins fall in true palæoblattarian fashion on the inner margin, while in others which cannot be dissociated generically from them, the anal veins are disposed as in modern types. But in all there is a loss of one of the principal veins, or rather an amalgamation of two or more--a characteristic of more fundamental character. As a general rule, moreover, to which we shall again advert, the mass of the species are of small size, in very striking contrast to the older types. [Illustration: Fig. 122.--_Neorthroblattina Lakesii_ Scudd. × 5. Trias, Colorado.]