Dr. ir. A. Nicholson on neio S^yecies of GrajJtolites. 241 



curved. The cclhiles are about eighteen in the space of an 

 inch, and are indisting-uishable in all their characters from 

 those of G. N^ilssoni, Barr. They are long, naiTOAv, and so 

 arranged that they do not overlap one another at all ; the outer 

 cell-walls being inclined to the axis at an angle of not more 

 than 15° to 20°, and being three to four times as long as the 

 cell-mouths, the latter forming short ti'ansverse apertures at 

 right angles to the axis. 



This pretty little species is readily separated from all allied 

 forms (such as D. )iitn7us, Hall, and JJ. serratidus^ Hall) by 

 the remote free cellules, "U'liich do not overlap one another, by 

 the general shape of the frond, and by the small length and 

 great tenuity of the stipes. 



Loc. Lower beds of the Skiddaw Slates, Barff, near Kes- 

 wick. Upper beds of the vSkiddaw Slates, EUergill, near !Mil- 

 bum ,• and Eggbeck, near Pooley. 



Didymograpsusfascicidatus^ Nicli. PI. XI. figs. 21 & 22. 



Spec. char. Frond consisting of two simple stipes arising 

 from a short obtuse radicle. The stipes are at first directed 

 horizontally outAvards, but are immediately bent downwards 

 towards the radicle, again curving horizontally outwards. 

 The cellules occupy the concave face of each stipe, forming 

 thus the angle of divergence ; but, owing to the cmwature of 

 the stipes, the amount of this angle can hardly be stated. 

 Each stipe is extremely narrow at first, but gradually widens 

 out till a breadth of nearly one twenty-fourth of an inch may 

 be reached. The common canal is very narrow, but is Avider 

 than the cellules. The cellules are excessively long and nar- 

 row, curved, following the curvature of the stipe, the cell- 

 mouths being at right angles to the axis of the cellules. The 

 cell-mouths are not more tlian about twenty-four in the space of 

 an inch in the adult portion of the stipe, and the cellules overlap 

 one another for fully two-tliirds of their entire length. An indi- 

 vidual cellule, when fully grown, may have the extraordinary 

 length of more than two lines, with a uniform breadth of not 

 more than one-hundredth of an inch. Owing to the great 

 length and narrowness of the cellules, and owing to their 

 inclination being so small that they are nearly parallel to the 

 back of the stipe, the cellules in the distal portion of the stipe 

 appear to form a bundle of long narrow tubes. In consequence 

 of this, a line draAvn at right angles to the distal ])ortion of the 

 stipe would exhibit a section of three, or even four, cellules. 



This species cannot be confounded with any other, being 

 distinguished by the curiously cinved stipes with the cellules 

 on their concave aspect, the latter being nearly parallel to the 



