DESCRIPTION OF SPECIES. 33 



nules of A. rhombifolius. Plate XIII, Fig. 3a, represents two pinnules of the 

 lower part of the plant, and Fig. 3 b, two from the upper part, both magnified 

 to show the nervation. The fertile plant was not found. 



Formation and locality. — Found at Clover Hill only, in strata between 

 the main and lower coal seams. 



Acrostichides microphyllus, spec. nov. 



Plate VII, Fig. 5; Plate X, Fig. 2; Plate XI, Fig. 4; Plate XII, Fig. 3. 



Frond bi- or tripiunate. Fertile frond not seen, sterile frond, or primary pinna, 

 with a rachis having on the upper face a raised line on each side bordering a chan- 

 nel, and on the under side convex. Ultimate pinna? subopposite or alternate, distant, 

 inserted at an angle of about 45°, very long, slender, and linear in form. Pinnules 

 subopposite or alternate, very small, thick, and rather coriaceous, subrhombic or 

 subquadrilateral in shape, inserted by the entire base on the rachis of the ultimate 

 pinnse which has a raised margin on each side. The lower pinnule on the lower side is 

 often inserted half on the principal rachis. Nerves in about three groups, departing 

 from a common point of insertion situated rear the lower part of the pinnule, each 

 group branching freely, the lower group sending off branches only on the lower side, 

 the lowest of which curve strongly to meet the margin of the pinnule. 



In many features this beautiful little plant resembles A. rhombifolius, 

 and it evidently belongs to the same type of Acrostichides. It seems, how- 

 ever, to be specifically distinct, for the small size of the pinnules, and the 

 linear, almost thread-like nature of the pinna? of the ultimate order, are 

 constant features, so that a specimen may be recognized at a glance. The 

 stoutness of the principal rachis in Plate VII, Fig. 5, shows that this speci- 

 men belongs to the lower part of the frond, and if the plant be merely a 

 small form of A. rhombifolius, the pinnules here should be of the normal 

 size as seen in A. rhombifolius. The nervation is more slender than that of A. 

 rhombifolius, and owing to the thickness of the leaf substance, cannot be seen 

 distinctly in many cases. The very long and slender primary pinna shown in 

 Plate X, Fig. 2, and the smaller form seen in Plate XI, Fig. 4, appear to 

 belong to a different species from that represented in Plate VII, Fig. 5, and 

 Plate XII, Fig. 3. These last mentioned forms show the nerves distinctly 

 and sharply defined, though the leaf substance is thick and the nerves del- 

 icate. The slender specimens given in Plate X, Fig. 2, and Plate XI, Fig. 

 4, do not show any nerves, and the epidermis is very thick and coriaceous. 

 These long and slender pinnae, both primary and secondary, cover the 

 3f 



