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[2] 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].
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.
This Wealden fern[839] has been doubtfully assigned to the Schizaeaceae on the ground of the resemblance of the sterile fronds to those of some species of Aneimia, and because of the difference between the sterile and fertile pinnae (Fig. 260). Ruffordia cannot be regarded as a well authenticated member of the Schizaeaceae.