Fig. 256.

[B, C, from specimens (13491; 39234) in the British Museum (B, very slightly reduced; C, ½ nat. size); D, E, after Zeiller; F, after Renault; G, after Raciborski.]

It is hopeless to attempt to arrive at satisfactory conclusions in regard to the applicability of the name Todites Williamsoni to the numerous fronds from Jurassic and Rhaetic rocks, agreeing more or less closely with Brongniart’s type-specimen. Specimens from the Rhaetic may not be specifically identical with those from the Jurassic; the main point is that, whether actually identical or not, both sets of fossils clearly represent the same general type of Osmundaceous fern[798] and may for present purposes be included under the same designation. The above synonymy, though by no means complete[799], serves to illustrate the confusion which has existed in regard to this widely spread type of Mesozoic fern.

Todites Williamsoni may be briefly described as follows:—

Frond bipinnate; long linear pinnae (20–30 cm.) of uniform breadth arise at an acute angle, or in the lower part of a frond, almost at right angles, from a stout rachis. Closely set pinnules attached by a broad base; slightly falcate, the side towards the rachis strongly convex and the outer margin straight or concave and bulged outwards towards the base of each segment, margin usually entire, or it may be slightly lobed. Fertile pinnules similar to the sterile; sporangia of the Osmundaceous type and often scattered over the whole lower surface of the lamina ([fig. 256], B, B′, G). Venation of the Cladophlebis type (cf. [fig. 256], A).

It is not always easy to distinguish Todites Williamsoni from Cladophlebis denticulata, another common Jurassic fern, but in the latter the pinnules are usually longer and relatively narrower and the rachis is more slender (cf. [fig. 256], B and 257). Schenk[800] and Raciborski[801] have shown that the sporangia of Todites conform in the absence of a true annulus to those of Todea ([fig. 256], G) and Osmunda. Nathorst[802] has recently figured a group of spores of Todites Williamsoni in illustration of the use of the treatment of carbonised impressions with nitric acid and potassium chlorate. This species, though widely distributed in Jurassic rocks, is hardly distinguishable from the German Rhaetic fronds figured by Schenk from Bayreuth as Acrostichites Goeppertianus[803], or from other fossils referred to an unnecessarily large number of species by Fontaine[804] from Upper Triassic rocks of Virginia[805].

It would seem from the paucity of later records of Osmundaceae that the family reached its zenith in the Jurassic era. When we pass to the later Tertiary and more recent deposits evidence is afforded in regard to the geographical range of Osmunda regalis. It has been shown to occur in the Pliocene forest-bed of Norfolk[806] as well as in Palaeolithic and Neolithic deposits[807].