The genus _Dipteris_, formerly included in the Polypodiaceae, has been assigned to a separate family partly on account of the slight obliquity of the vertical annulus (fig. 231, G) and on other grounds[702]. The four species _Dipteris conjugata_, _D. Wallichii_, _D. Lobbiana_ (= _D. bifurcata_), and D. _quinquefurcata_ (fig. 231) are characterised by a creeping rhizome bearing fronds reaching a length of 50 cm.; in _D. conjugata_ and _D. Wallichii_ the lamina is divided by a median sinus into two symmetrical halves, while in other species the leaf is dissected into narrow linear segments. The main dichotomously branched ribs are connected by lateral branches and these by tertiary veins, the delicate branches of which end freely within the square or polygonal areolae (fig. 231, A′, E). The naked sori are composed of numerous sporangia and filamentous hairs: while in some species the soral development conforms to that characteristic of the Mixtae, it has been shown that in one species, _D. Lobbiana_ (= _D. bifurcata_[703]), the sporangia develope simultaneously as in the Simplices. _Dipteris_ occurs in company with _Matonia_ on Mt Ophir and elsewhere in the Malay peninsula; it extends to the Philippines, Samoa, New Caledonia, China, New Guinea, and the subtropical regions of Northern India. • • • • • The impossibility of drawing a hard and fast line between the divisions adopted in any system of classification is well illustrated by the ferns. In the main, the three-fold grouping suggested by Bower is probably consistent with the order of evolution of the true ferns. The Polypodiaceae, which are now the dominant group, are in all probability of comparatively recent origin, while the Gradatae and Simplices represent smaller subdivisions with representatives in remote geological epochs. The genera _Loxsoma_, _Matonia_ and _Dipteris_ afford examples of ferns exhibiting points of contact with more than one of Bower’s subdivisions: they are generalised types which, like many relics of the past, are now characterised by a restricted geographical range. [Sidenote: RECENT FERNS] [Illustration: FIG. 232. _Davallia aculeata._ (⅖ nat. size.)]