140 PROCEEDINGS OP THE GEOLOGICAL SOCLETT. 



upper part of the Skiddaw Slates, and does not occur in their lower 

 portion. D. teretiusculus, His., belongs to that group of Diplograpsi 

 in which the axis is prolonged below the proximal extremity of the 

 frond in the form of a long and slender radicle. The cellules are 

 simply excavated in the sides of the polypidom ; and all specimens 

 appear either as scalariform impressions, or in the form described by 

 M'Coy under the name of D. rectangularis. This species is, however, 

 too well known to require any description. 



Log. Common and well preserved in the soft black shale of EUer- 

 gill Beck, near Milbum, in Westmoreland. 



20. DiPLOGRAPSus PEiSTrPTiEOEMis, Hall, sp. PI. Y. figs. 14 & 15. 



Graptolithus pristiniformis, Hall, Grapt. Quebec Group, p. 110, 

 pi. 13. figs. 15-17. 



This is a Quebec species, which is of very common occurrence in 

 the Skiddaw Slates, and is probably the same as the one which was 

 doubtfully referred to D. pristis, His., by llr. Salter in his note on 

 the Graptolites of this formation. (Quart. Journ. Geol. Soc. vol. xix.) 

 It is, however, distinguished from D. pristis, His., by the smaller 

 width of the frond, by the greater number of cellules in an inch, 

 and by the character of the base. 



The frond is simple, diprionidian, and varying in length from | 

 to 1^ inch. It tapers gradually towards the base, the width in the 

 fully developed portion being from -^ig- to -^ of an inch. The base 

 is furnished with a slender radicle, the length of which varies from 

 -^ to nearly -^ of an inch, the cellules sometimes commencing quite 

 abruptly, sometimes tapering ofi" into the radicle. The cellules are 

 very narrow and closely set, being from 28 to 35 in the space of an 

 inch, inclined to the axis at the very low angle of about 20°, and 

 having about one-third of their length free. The denticles alternate 

 distinctly with one another, their extremities being sometimes acute 

 and sometimes rounded, perhaps more commbnly the latter. The 

 axis is generally prolonged beyond the distal extremity of the frond. 

 In one very beautiful specimen, apparently of this species, from the 

 upper beds of the Skiddaw Slates, the apices of the cellules are pro- 

 vided with small mucrones or spines, which have an upward direction. 

 (PL Y. fig. 22.) 



This species is somewhat like I), angustifolius, HaU, but is dis- 

 tinguished by the fact that the cellules in the latter are not markedly 

 alternate, and are always rounded, whilst the base is provided (as in 

 D. pristis. His.) with three processes. 



Loc. Outerside, near Keswick (lower beds of the series) ; Ellergill, 

 near Milburn, Westmoreland (upper beds of the series). 



Genus Graptolites vel Geaptolithfs, Linn. 



This genus should properly be confined to those Graptolites which 

 consist of a simple stipe, with a single row of cellules on one side. 

 The base or commencement of the stipe is marked by a small 

 radicle, and is generally curved, the cellules not attaining their fuU 



