The _Pecopteris_ (Fig. 4, _P. heterophylla_) or comb-fern, is so called from its stiff thick leaflets being in some species arranged along the stalk like the teeth along the centre of a comb. Of all the plants of the coal-measures this is the one that approaches most closely to living nature. It appears to be almost identical with the _pteris_, of which one species is well known as the bracken of our hill-sides. Dr. Hooker figures together a frond of a New Zealand species (_P. esculenta_) and a fossil frond from the Newcastle pits. They are so similar as to be easily mistaken at first sight for drawings of the same plant.[17] The _Neuropteris_ (as _N. gigantea_, Fig. 6) or nerve-leaved fern, is remarkable for its strongly-defined venation. It is scarcely, perhaps, so elegant in its outline as the _sphenopteris_, or some of the other ferns. Its leaflets are large and thick, with an oblong or rounded form, and arranged either singly along the frond stem, or along secondary foot-stalks, which diverge from the main stem. Of the latter kind, some of the species have a good deal of resemblance to our _Osmunda regalis_ or royal fern. A species of the former class (_N. cordata_) might readily enough be mistaken for the young leaves of the _Scolopendrium_ or hart's-tongue, which hangs out its glossy green amid the gloom of dank and dripping rocks. There are, besides, several other genera of ferns in the Carboniferous strata, such as the _Cyclopteris_ (_C. dilatata_, Fig. 5) or round-leaved fern, and the _Odontopteris_ or tooth-fern. Most of these seem to have been lowly plants, like the ferns of our own country. But there was another class to which no analogue can be shown in Europe. They rose high over their humbler congeners as lofty trees, and must be studied by a reference to the existing tree-ferns of intertropical countries. [Footnote 17: Hooker, _Mem. Geol. Surv._ vol. ii. part ii. p. 400.] [Illustration: Fig. 7. Living Tree-fern.]