It is not until we ascend the geological series as far as the older Jurassic rocks that we meet with a type which can with confidence be classed with the Schizaeaceae, as least so far as sporangial characters are concerned. The species _Klukia exilis_ is selected as the best known and most widely-spread representative of Jurassic Schizaeaceae. _Klukia exilis_ (Phillips)[829]. Fig. 259. The generic name _Klukia_ was proposed by Raciborski[830] for a species originally described by Phillips[831] from the Inferior Oolite of the Yorkshire coast as _Pecopteris exilis_. Bunbury’s[832] discovery (supplemented by additional evidence obtained by Raciborski) of well-preserved sporangia justified the substitution of a distinctive designation for the provisional term _Pecopteris_. [Illustration: FIG. 259. _Klukia exilis_ (Phillips). (Figs. 1–3, × 40; fig. 4, × 3; fig. 5, nat. size.)] The species may be defined as follows:— Frond tripinnate, of the _Cladophlebis_ type; pinnae linear, lanceolate, attached to the rachis at a wide angle. Ultimate segments short and linear, entire or, in the lower part of a frond, crenulate, 5 mm. long or occasionally longer. Sporangia 0·5 mm. in length, borne singly on the lower surface of the lamina in a row on each side of the midrib. A re-examination[833] of the specimen described by Bunbury confirmed his account of the structure of the sporangia. The pinna shown in fig. 259 is characterised by unusually small fertile pinnules some of which bear 10 sporangia in two rows; the annulus includes about 14 cells. Fertile specimens of this and similar forms are figured by Raciborski[834] from Jurassic rocks of Poland, and good examples of the English species may be seen in the Leckenby collection, Cambridge, in the British Museum, the museums of Manchester, Scarborough, and other places. It is possible that specimens referred to _K. exilis_ by Yokoyama[835] from Wealden strata in Japan may afford evidence of the persistence of the species beyond the Jurassic era, but in view of the close resemblance of the sterile fronds described from Wealden strata as _Cladophlebis Brownii_[836] and _C. Dunkeri_[836] to those of _Klukia exilis_, identity can be established only by an examination of fertile specimens. A Jurassic fern recently described by Yabe[837] from Korea as _Cladophlebis koraiensis_ may be identical with _K. exilis_ and there is little doubt as to the existence of the species in Jurassic Caucasian strata[838]. [Illustration: FIG. 260. _Ruffordia Goepperti_. (A, C, sterile; B, fertile; slightly reduced. Specimens from the Wealden of Sussex; British Museum; V. 2333, V. 2160, V. 2166.)] _Ruffordia Goepperti_ (Dunk.). Fig. 260.