It is a peculiarity of these ancient Insects that they were much larger creatures than the corresponding forms that now exist. This may be due, to some extent, to the fact that tiny, {344}fragile forms have not been preserved in the rocks, or have not attracted the attention of collectors; but as some of the palaeozoic Insects were absolutely the largest known—surpassing considerably in size any Insects at present existing—it is probable that, even if small forms existed at the remote epoch we are alluding to, the average size of the individual was greater than it is at present. The Megasecopterides of the carboniferous epoch were Insects of large size, with long, narrow wings, a small prothorax, and large meso- and meta-thorax, these two segments being equal in size; the abdomen was elongate and moderately voluminous, and was terminated by a pair of very elongate, slender filaments like those of the may-flies. The family includes several genera and species found at Commentry. One of these forms, _Corydaloides scudderi_, is of great interest, as it is believed by Brongniart that the imago possessed tracheal gills situated on the sides of the abdomen, analogous with those that exist at present in the immature condition of certain Ephemeridae. They are of interest in connexion with the gills found at the present time in the imagos of _Pteronarcys_ (see p. 401). Although these fossils are of such enormous antiquity, the tracheae can, M. Brongniart says, be still perceived in these processes. The Platypterides include also a considerable number of Insects of large size, with four large equal wings, frequently spotted or variegate. Some of these Insects were provided with expansions or lobes on the sides of the prothorax (Fig. 213); these are looked on as analogous to the expansions of meso- and meta-thorax, which are supposed by some writers to have been the rudiments from which wings were developed. These prothoracic wing-rudiments, if such they be, are said to have a system of nervures similar to what we find in true wings. The genus _Lithomantis_ includes a Scotch fossil, and has already been mentioned by us on p. 259. [Illustration: FIG. 213.—_Lithomantis carbonaria_. Carboniferous strata of Commentry, France. (After Brongniart.)] The third family of extinct carboniferous Neuroptera is the Stenodictyopterides, in which Brongniart places the _Dictyoneura_ of {345}Goldenberg, the North American _Haplophlebium_, and several genera from Commentry. Some of them were very large Insects, with robust bodies, and possessed wing-like expansions on the prothorax, and lateral gill-like appendages on the sides of the abdomen. It is worthy of note that though so large a number of carboniferous Neuroptera have now been discovered, no larvae or immature forms have been found. We now pass to the consideration of the divisions of Neuroptera still living. FAM. I. MALLOPHAGA—BIRD-LICE OR BITING LICE.