Dictyophyllum rugosum, Lind. and Hutt. Fig. 283.
| 1828. | Phlebopteris Phillipsii, Brongniart, Hist. vég. foss. p. 377, Pl. CXXXII. fig. 3; Pl. CXXXIII. fig. 1. |
| 1829. | Phyllites nervulosis, Phillips, Geol. Yorks. p. 148, Pl. VIII. fig. 9. |
| 1834. | Dictyophyllum rugosum, Lindley and Hutton, Foss. Flor. II. Pl. CIV. |
| 1836. | Polypodites heracleifolius, Goeppert, Foss. Farn. p. 344. |
| 1849. | Camptopteris Phillipsii, Brongniart, Tableau, p. 105. |
| 1880. | Clathropteris whitbyensis, Nathorst, Berättelse, p. 83. |
This species, which is characteristic of Jurassic rocks, is less completely known than the two types described above, but in the form and venation of the pinnae there is little difference between the Rhaetic and Jurassic plants. The leaves of the Jurassic species appear to have been smaller and more like those of Dipteris conjugata ([fig. 231]); there are no indications of the existence of the two curved arms at the summit of the petiole which form so striking a feature in D. exile and D. Nathorsti. No sporangia have been found on English specimens, but it is safe to assume their agreement with those of other species. A more complete list of records of D. rugosum is given in the first volume of the British Museum Catalogue of Jurassic plants[950].
Fig. 283. Dictyophyllum rugosum (Lind. and Hutt.). (Brit. Mus. Nat. size.)
Nathorst[951] has recently drawn attention to certain differences between Dictyophyllum and Dipteris. The pinnate division of the pinnae is not represented in the fronds of the recent species, but this method of lobing, which is a marked characteristic of Dictyophyllum, is less prominent in Clathropteris; and in Camptopteris lunzensis Stur[952], an Austrian Upper Triassic species, the pinnae are entire. In Dictyophyllum the sori cover the whole lower surface of the leaf; in Dipteris they are more widely separated and the sporangia have a diameter of 0·02 mm., but in Dictyophyllum the diameter is 0·4–0·6 mm. Moreover in Dictyophyllum the sori contain 5 to 8 sporangia, whereas in Dipteris they are much more numerous. Despite these differences it is clear, as Nathorst says, that Dictyophyllum, Clathropteris, and Camptopteris are existing types very closely allied to Dipteris. It is a matter of secondary importance whether we include all in the Dipteridinae or follow Nathorst’s suggestion and refer the fossil genera to the separate family Camptopteridinae.
Thaumatopteris.
This genus, founded by Goeppert[953] for a Rhaetic plant from Bayreuth, is by some authors[954] regarded as identical with Dictyophyllum, but it has recently been resuscitated by Nathorst[955] for specimens which he names T. Schenki, formerly included by Schenk in his species T. Brauniana[956]. It bears a close resemblance, in the long linear pinnules with an entire or crenulate margin, to Dictyophyllum Fuchsi described by Zeiller[957] from Tonkin, and it would seem hardly necessary to adopt a distinctive generic designation. The sporangia have a vertical or slightly oblique annulus and the rhizome is similar to that of Dictyophyllum exile. The habit of the genus is shown in [fig. 284], which represents one of the German Rhaetic species.
Fig. 284. Thaumatopteris Münsteri. (From a specimen in the Bergakademie, Berlin; ⅓ nat. size.)