3. Sphenophyllum Thoni Mahr. Fig. 110, A.
Another type of Sphenophyllum is illustrated by S. Thoni Mahr as shown in fig. 110, A. This species was first described by Mahr[915] from the Coal-Measures of Ilmenau, and has since been figured by Zeiller and other authors. Each whorl consists of six large obcuneiform leaves with the broad margin somewhat irregularly fringed. The unusually good specimen of which fig. 110, A, represents a single verticil was originally described and figured by Zeiller in 1880[916]; it is now in the École des Mines Museum, Paris.
Fig. 110.
- Sphenophyllum Thoni, Mahr. (After Zeiller.)
- Sphenophyllum trichomatosum, Stur. From a specimen in the Woodwardian Museum; from the Coal-Measures of Barnsley, Yorks. A and B ¾ nat. size.
The leaf-forms illustrated by figs. 109 and 110 are some of the more extreme types of Sphenophyllum leaves; but these are more or less connected by a series of intermediate forms. For a more complete systematic account of the different species the student should consult such works as those by Coemans and Kickx[917], Zeiller, Schimper, and others.
4. Sphenophyllum speciosum (Royle). Fig. 111.
1834. Trizygia speciosa, Royle[918].
The species shown in fig. 111 has been usually described as a separate genus Trizygia, a name instituted by Royle in 1834 for some Indian fossils from the Lower Gondwana rocks of India[919]. Zeiller[920] has lately pointed out the advisability of including this Asiatic type in the genus Sphenophyllum. The slender stem bears verticils of cuneate leaves in three pairs at each node, the anterior pair being smaller than the two lateral pairs. The characteristic Sphenophyllum venation is clearly seen in the enlarged leaf, fig. 111, B.
