342 Dr. H. A. Nicholson on the British 



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

 axis. 



Of this species I have only a single exani])le, which I have 

 recently oljtained from the Skiildaw 81atcs ; 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 

 Quel)ee form. In most characters D. exfensus agrees with D. 

 patuIuSj especially in the sha])c of the frond ; the two forms, 

 however, appear to be satisfactorily separated by some minor 

 but constant differences. The stipes are altogether much 

 more slender than in D. patidus-^ the cellules are slightly fewer 

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

 are not prolonged into markedly submucronate ])oints. To 

 show these differences, 1 have reproduced Hall's enlarged 

 figures of fragments of the two forms (PL YII. figs, 1 a & 

 2 a). 



Loc. Skiddaw Slates, Outerside, near Keswick. 



Didymograpsus nitiduSj Hall, sp. Fig. 3. 



GraptoUthus nitiilm, Hall (Grapt. Quebec Group, p. 69, pi. 1. figs. 1-9). 

 Di(Ii/mo(/rupsus nitidns (Nicholson, Quart. .Tourn. Geol. Soc. vol. xxiv. 

 p." 13.^). 



Also figiu-ed, but not named or described, by ]\Ir. Salter in 

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



Frond composed of two simple stijies 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 wnden 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 ; b, 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 s])ace 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- 

 Avalls. 



This exceedingly pretty little species occurs pretty abun- 



