Fig. 19.
The Sphenopteris tridactylites, which exhibits in the arrangement of its fronds one of the most symmetrical forms to be found among this elegant class of plants, can scarcely be sufficiently exhibited in the space we are enabled to afford. It is abundant in the shales of the mines of Montrelais. In the same district is also found the Neuropteris Heterophylla ([Fig. 20]), which is remarkable for the arrangement of its fleshy leaves and the regularity of its venations. It must be remembered that our drawing only represents one of the fronds. The grouping of the whole on the straight and slender stem is very beautiful.
Fig. 20.
The Pecopteris Whitbiensis ([Fig. 21]), which presents many differences from the other forms, is copied from a specimen found in a nodule of argillaceous ironstone from the lower shale at Cloughton, and certainly it presents many points of interest.
Among the most remarkable and characteristic plants of the coal formation is the Sigillaria, of which extraordinary trailing plant upwards of sixty species have been described.
