The specimen on which this species was founded was discovered in the Nubian Sandstone east of Edfu; the age of the beds is uncertain, but the presence of Clathropteris suggests a Lower Jurassic or Rhaetic horizon[963]. Seven strong ribs radiate through the lamina from the summit of the petiole; at a and b small pieces of the projecting ribs are shown in the grooves. From the main veins slender branches are given off at right angles and, as seen in the enlarged drawing, these again subdivide into a delicate reticulum with free-ending veinlets.
Fig. 287. Camptopteris spiralis. (After Nathorst. Much reduced.)
Camptopteris.
Camptopteris spiralis, Nath. Figs. [282], C; [287].
Nathorst proposed this generic name for Rhaetic fronds[964] resembling those of Clathropteris and Dictyophyllum, but differing in the form of the pinnae and in habit. The habit of the type-species, C. spiralis, is shown in [fig. 287]. An examination of the specimens in the Stockholm Museum convinced me of the correctness of Nathorst’s restoration[965]. Each of the forked arms of the rachis bore as many as 150–160 long and narrow pinnae characterised by an anastomosing venation ([fig. 282], C) and by a spiral disposition due to the torsion of the axes. The sporangia agree in essentials with those of Dictyophyllum.
Hausmannia.
A critical and exhaustive account of this genus has been given by Prof. Von Richter[966] based on an examination of specimens found in the Lower Cretaceous rocks of Quedlinburg in Germany. The name was proposed by Dunker[967] for leaves from the Wealden of Germany characterised by a deeply dissected dichotomously branched lamina. Andrae subsequently instituted the genus Protorhipis[968] for suborbicular leaves with dichotomously branched ribs from the Lias of Steierdorf. A similar but smaller type of leaf was afterwards described by Zigno[969] from Jurassic beds of Italy as P. asarifolius, and Nathorst[970] figured a closely allied form from Rhaetic rocks of Sweden. While some authors regarded Hausmannia and Protorhipis as ferns, others compared them with the leaves of Baiera (Ginkgoales); Saporta suggested a dicotyledonous affinity for leaves of the Protorhipis type. The true nature of the fossils was recognised by Zeiller[971], who called attention to the very close resemblance in habit and in soral characters to the recent genus Dipteris. A comparison of the different species of Dipteris, including young leaves ([fig. 231], p. 297), with those of the fossil species reveals a very striking agreement[972]. There can be no doubt, as Richter points out, that the names Hausmannia and Protorhipis stand for one generic type.
Hausmannia may be defined as follows:
Rhizome creeping, slender, dichotomously branched; leaf-stalks slender (2–25 cm. long), bearing a leathery lamina (1–12 cm. long and broad), wedge-shaped below, occasionally cordate or reniform, entire or more or less deeply lobed into broad linear segments. The leaf is characterised by dichotomously branched main ribs which arise from the summit of the rachis as two divergent arms and radiate in a palmate manner, with repeated forking, through the lamina. Lateral veins are given off at a wide angle, and, by subdivision, form a fairly regular network similar to that in Dictyophyllum, Clathropteris, and Dipteris.