DESCBIPTION OF SPECIES. 35 



Mertensides, gen. nov. 



Frond bi- or tripinnate, pinnae of ultimate order, subopposite or alternate, long, 

 and linear-lanceolate. Pinnules alternate, inserted at right angles, or nearly so, to 

 the rachis of the ultimate pinnae, fertile ones obtuse, sterile ones somewhat acute, all 

 subfalcate and distinct to the base, except in the upper part of the primary pinnae or 

 fronds. Middle nerve of the pinnules dissolved towards the apex into branches, 

 lateral nerves going off obliquely, the lower ones several times branched, the upper 

 ones branching less often. Fructification in the form of large globose sori inserted on 

 a branch of the lateral nerves, or on the summit of an unbranched lateral nerve, and 

 composed of from 4 to 6 sporangia grouped around a central axis. Sori mostly con- 

 fined to the lower half of the pinnules. Type, Mertensides bullatus, Pecopteris bullata 

 of Bunbnry. 



The plants which I have grouped under the generic name of Merten- 

 sides have a great resemblance to the Mertensia group of the Gleicheniacese. 

 The resemblance is sufficiently great, I think, to entitle these plants to 

 rank as the precursors, and representatives of the Gleicheniacese, which, 

 as Heer has shown, appear in force in the lowest Cretaceous beds of Green- 

 land. The only point of difference between our plants and Mertensia, is in 

 the absence of the dichotomous branching in Mertensides. They show a 

 strong resemblance to Asterocarpus, but in Mertensides the fructification as 

 a rule does not cover the whole pinnule, the upper portion being commonly 

 free, and showing the nervation distinctly. 



Mertensides bullatus (Buub. spec). 



Plate XV, Figs. 2 to 5 ; Plate XVI, Figs 1 to 3 ; Plate XVII, Figs. 1,2; Plate XVIII, Figs. 1,2; Plate 



XIX, Fig. 1. 



Frond bi- or tripinnate, perhaps arborescent. Principal rachis marked on the 

 upper face with a strong ridge near the margin on each border, on the lower face 

 rounded or cylindrical ; ultimate pinnae alternate, with a broad, fiat rachis, having a 

 strong woody cord running through the center of it, to which the middle nerves of the 

 pinnules are attached, sterile and fertile pinnules slightly differing in form, but both 

 with a thick leaf-substance; sterile pinnules rather more obliquely placed on the 

 rachis than the fertile ones, and more acute and falcate; fertile pinnules inserted 

 nearly or quite at right angles to the rachis of the ultimate pinna?, oblong, with a 

 slightly broadened base, bluntly rounded at the apex ; pinnules of both sterile and 

 fertile forms on the lower ultimate pinnae, crenately notched on the margin ; pinnules 

 on the upper ultimate pinnas, and toward the summit of the plant, united at base for 

 a greater or less distance ; those of the middle portions of the plant, or the normal 

 pinnules, separate to the base, all inserted by the whole of the slightly widened base, 

 on a rachis which appears to have been bordered by a thick coriaceous band, which 

 causes it to appear much thicker than it really is. Lowest pinnule, on the lower side 



