Species q/" Didjmograpsiis. 345 



obtuse radicle, at a primary angle of aboirt 330°, but after- 

 wards curved away from the radicle, so as to become nearly 

 horizontal. The angle of divergence of the stipes may there- 

 fore be stated upon the whole as 180°. The sti])es are ex- 

 tremely narrow at first, but widen out till a width of one- 



Fig. 6. 



a, Didymograpsus fasckulatus, from the Skiddaw Slates, restored ; b, a 

 fragment, enlarged. The inclmation of the cellules to the axis is too 

 great in these figures, 



twenty-fourth of an inch or more may be attained. The 

 cellules are on the opposite side of the frond to the radicle, or 

 occupy the sides of the angle of divergence. They are ex- 

 cessively long and narrow, about twenty-four in the space of 

 an inch, curved in accordance with the curvature of the stipes, 

 overlapping one another for fitlly two-thirds of their entire 

 length, the cell-mouths being at right angles to the axis. 

 The common canal is extremely naiTOw. 



The materials in my possession for a diagnosis of this spe- 

 cies are not satisfactory. Those specimens which exhibit the 

 general form of the frond are too ill-preserved for a proper 

 detemiination of the cellules ; and those which exhibit the 

 cellules are all fragments broken off close to the radicle. I 

 am, however, fully satisfied of the identity of the two sets of 

 specimens, and have therefore ventured to restore the species 

 provisionally, in the hope of shortly obtaining more perfect 

 examples. 



Loc. Upper beds of the Skiddaw Slates : Ellergill, near 

 Milburn ; Thomship Beck, near Shap ; and Eggbeck, near 

 Pooley. 



Didi/jnograjjsiis geminus, His. Fig. 6. 



(See Hisinger, Lethfea Suecica, pi. 38. fig. 3 ; .Salter, Quart. 

 Journ. Geol. Soc. vol. xix. p. 137, fig. 13 c, and Mem. Geol. 

 Survey, vol. iii. pi. 11 li. tig. 8; Nicholson, Quart. Journ. 

 Geol. Soc. vol. xxiv. p. 134, pi. 5. figs. 8-10.) 



Frond consisting of two small stipes springing from a long 

 and slender radicle, at an angle of divergence which is primi- 

 tively about 15°. The base is almost always more or less 

 rounded ; and the stipes very rapidly become parallel or sub- 



