342 Dr. H. A. Nicholson on the British 



nate, the cell-mouths making an angle of about 100° Avith the 

 axis. 



Of this species I have only a single example, which I have 

 recently obtained from the SkiddaAV Slates ; but its state of 

 preservation is better than that of most of the Graptolites of 

 this formation, and I have no doubt as to its identity with the 

 Quebec form. In most characters D. extenstts agrees with D. 

 patulus, especially in the shape of the frond ; the two forms, 

 however, appear to be satisfactorily separated by some minor 

 but constant diiferenccs. The stipes are altogether much 

 more slender than in I). jxUulns- the cellules are slightly fewer 

 to the inch, and make a smaller angle with the axis, and they 

 are not prolonged into markedly submucronate points. To 

 show these differences, I have reproduced Hall's enlarged 

 figures of fragments of the two forms (PI. VII. figs. 1 a & 

 2 a). 



Loc. Skiddaw Slates, Outerside, near Keswick. 



Didpnoffrapstcs mtidus. Hall, sp. Fig. 3. 



Graptolithus nitidus, Hall (Grapt. Quebec Group, p. 09, pi. 1. figs. 1-9). 

 Dkhjmoqrapsus nitidus (Nicholson, Quart. Jouru. Geol. See. vol. xxiv. 

 p. 135). 



Also figured, but not named or described, by Mr. Salter in 

 the Quart. Journ. Geol. Soc. vol. xix. p. 137, fig. 13 d. 



Frond composed of two simple stipes proceeding from a 

 small pointed radicle at an angle of 150° to 175°. The stipes 

 vary in length from one-half to three-quarters of an inch, and 

 are very narrow at their commencement, but widen out till a 

 width of from one-twentieth to one-fifteenth of an inch may be 



Fig. 3. 



a, Didymograpsus nitidus, from the Skiddaw Slates, nat. size ; h, a smaller 

 example, slightly enlarged ; c, fragment, enlarged, to show the cellules. 



attained. The cellules are on the opposite side of the frond to 

 the radicle, or occupy the sides of the angle of divergence. 

 They vary from thirty-two to thirty-four in the space of an 

 inch, and are inclined to the axis at an angle of from 40° to 

 45°. The denticles are simply angular, and are not submucro- 

 nate, and the cell-mouths are nearly at right angles to the cell- 

 walls. 



This exceedingly pretty little species occurs pretty abun- 



