134 PROCEEDINGS OF THE GEOLOGIGAI SOCIETY. 



were visible in full, whilst the apparent radicle was consti- 

 tuted by a small portion of a third stipe. Whether this explana- 

 tion applies to the specimens originally described by Mr. Salter, I 

 do not, of course, pretend to say, though the probabilities are in its 

 favour. Certainly, in a large series of specimens from the Skiddaw 

 Slates, I have been able to find none in which it would not account 

 for the phenomena observed. Whilst it is possible, therefore, that 

 there may really exist a distinct species with the characters of D. 

 caduceus, Salt., it certainly appears not to occur in the Skiddaw 

 Slates, since all specimens which could be referred to this species, 

 when well preserved, show traces of a third, and even sometimes of 

 a fourth, stipe. 



10. DrDTMOGRAPSTJS Y-rRACTUS, Salt. (Quart. Journ. Geol. Soc. 

 vol. xix. p. 137, f. 13 e.) 



This rare and elegant species is characterized by the fact that 

 the stipes, after proceeding upwards from the short radicle, bend 

 abruptly outwards, so as to enclose a much more open angle than 

 the primary angle of divergence. In all other particulars it is 

 almost, if not quite, identical with D. joatulus, Hall (=i). hirundo, 

 Salt.), of which it may possibly be a variety. The ceUules are on 

 the upper or inner side of the frond, i. e. on the side remote from 

 the radicle, and appear to resemble in shape those common to the 

 majority of the Skiddaw Graptolites, being long, narrow, and pro- 

 vided with a strong submucronate extension of the proximal lip of 

 the cell-aperture. The species is said by Mr. Salter to be closely 

 allied to D. Pantoni, M'Coy, from the Graptolitiferous rocks of Yic- 

 toria. 



11. DinrMOGEAPSTJS SEXTAINS, HaU. Pal. New York, vol. i. p. 273, 

 pi. 74. fig. 3. 



B. sextans is given by Mr. Salter in his list of Graptolites from the 

 Skiddaw Slates ; but I have never seen any specimen of it from this 

 horizon. It is somewhat peculiar among the Didymograpsi, from 

 the fact that the cellules are placed on the lower or outer side of 

 the frond, i. e. on the same side as the radicle. It occurs in the 

 Utica Slate in America (Caradoc), and in great abundance in cer- 

 tain beds in Dumfriesshire (Upper Llandeilo), and it is too well 

 known to need description. 



Log. Braithwaite Brow. 



12. DiDYMOGEAPSus GEMiNus, Hisiuger (Leth. Suecica, Supp. ii.). 

 P1.Y. figs. 8-10. 



This well-known Swedish species occurs very plentifully in the 

 -Skiddaw Slates, though seldom well preserved. The form usually 

 figured as D. geminus (see ' Siluria ' Fossils 8. fig. 8, and Lyell's 

 ' Elements,' p. 563, fig. 656) is in reality D. patulus, Hall ( = b. hi- 

 rundo, Salt.). In the true species the frond consists of two small 

 stipes arising from a long and slender radicle, at first curving out- 

 wards, and then running more or less nearly parallel with one 



