In endeavouring to distinguish specifically between fronds showing a general agreement in habit with _C. denticulata_, special attention should be paid to venation characters, the shape of the pinnules, the relation of the two edges of the lamina to one another, and to the amount of curvature of the whole pinnule. Unless the material is abundant, it is often impossible to distinguish between characters of specific value and others which are the expression of differences in age or of position on a large frond, to say nothing of the well-known variability which is amply illustrated by recent ferns. It is remarkable that very few specimens are known which throw any light on the nature of the fertile pinnae. Fig. 258 represents an impression from the Inferior Oolite rocks of the Yorkshire coast in which the exposed upper surface of the pinnules shows a series of parallel ridges following the course of the lateral veins and no doubt formed by oblong sori on the lower surface. There can be little doubt that the specimen figured by Lindley and Hutton and by others as _Pecopteris undans_[817] is, as Nathorst suggests, a portion of a fertile frond of _C. denticulata_. A fertile specimen of a frond resembling in habit _C. denticulata_, which Fontaine has described from the Jurassic rocks of Oregon as _Danaeopsis Storrsii_[818], exhibits, as that author points out, a superficial resemblance to the specimen named by Lindley and Hutton _Pecopteris undans_. There is, however, no adequate reason for referring the American fragment to the Marattiaceae. In the absence of sporangia we cannot speak confidently as to the systematic position of this common type; but there are fairly good grounds for the assertion that some at least of the fronds described under this name are those of Osmundaceae. The English specimen shown in fig. 258 is very similar to some Indian fossils figured by Feistmantel as _Asplenites macrocarpus_[819], which are probably identical with _Pecopteris australis_ Morris[820], a fern that is indistinguishable from _Cladophlebis denticulata_. Renault[821] figured a fertile specimen of the Australian fossil as _Todea australis_, which agrees very closely with that shown in fig. 258, and the sporangia figured by the French author are of the Osmundaceous type. Another example of a fertile specimen is afforded by a Rhaetic fern from Franconia, _Asplenites ottonis_, which is probably identical with _Alethopteris Roesserti_ Presl [= _Cladophlebis_ (_Todites_) _Roesserti_], a plant closely resembling _Cladophlebis denticulata_. Another argument in favour of including _C. denticulata_ in the Osmundaceae is supplied by the association of pinnae of this type with the petrified stem of _Osmundites Dunlopi_ recorded by Kidston and Gwynne-Vaughan. [Illustration: FIG. 258. Fertile pinnae of _Cladophlebis denticulata_. (From a Yorkshire specimen in the Sedgwick Museum, Cambridge.)] =Schizaeaceae.=