Among these mesozoic Cockroaches are some of very peculiar aspect; one, _Blattidium_ (see figure of _B. Simyrus_), found only in the lower Purbecks, has ribbon-shaped wings with parallel sides, longitudinal neuration, and anal nervures with a course at right angles to their usual direction; another, _Pterinoblattina_ (see figure of _P. intermixta_), geologically widespread, is very broad, more or less triangular, and has an exceedingly fine and delicate neuration, so arranged as to resemble the barbs of a feather. [Illustration: Fig. 124.--_Blattidium Simyrus_ Westw. × 3. Lower Purbecks, England.] A comparison of the neuration of the tegmina of mesozoic and recent Cockroaches, to determine as far as possible the immediate relations of the former to existing types, gives as yet little satisfaction. The prolific genera, _Mesoblattina_ and _Rithma_, may be said to bear considerable resemblance to the _Phyllodromidæ_, and the peculiar neuration of _Elisama_ is in part repeated in the _Panchloridæ_, as well as in some _Phyllodromidæ_ and _Epilampridæ_. _Scutinoblattina_ also reminds one in certain features of some _Epilampridæ_, like _Phoraspis_. The other genera appear to have no special relations to any existing type. As a whole, it would appear as if the _Blattariæ spinosæ_ approached closer to the mesozoic forms than do the _Blattariæ muticæ_. [Illustration: Fig. 125.--_Pterinoblattina intermixta_ Scudd. × 4. Upper Lias, England.] As to the tertiary Cockroaches we know very little, exceedingly few having been preserved, even in amber--that wonderful treasury of fossil Insects. Here first we come across apterous forms, _Polyzosteria_ having been recognised in Prussian amber,[199] together with winged species, which seem to be _Phyllodromidæ_; these are the only _Blattariæ spinosæ_ known from the Tertiaries. Of the other group, we have _Zetobora_, one of the _Panchloridæ_, and _Paralatindia_, one of the _Corydidæ_, from American rocks, and _Heterogamia_ and _Homœogamia_, one from Parschlug in Steiermark, the other from Florissant in Colorado, belonging to the sub-family _Heterogamidæ_. Others are mentioned, generally under the wide generic term _Blatta_, from Oeningen, Eisleben, Rott, and even from Spitzbergen and Greenland; but little more than their names are known to us. _Paralatindia_, from the Green River beds of Wyoming, U.S., is the only tertiary Cockroach yet referred to an extinct genus; but close attention has not yet been paid even to the few tertiary Cockroaches which we know. There is no reason to suppose that they will be found to differ more from the existing types than is generally the case with other Insects. The more we learn of cænozoic Insects, the more truly do we find that the early Tertiary period was in truth the dawn of the present, the distinction between the faunas of these remotely separated times (though not to be compared in character) being scarcely greater than is found to-day