Vol. 54.] FATHTA OP THE SKIDDAW SLATES. 511 



but after the first divergence the stipes run more or less parallel 

 to each other, though there is in some forms a tendency to close 

 together at their distal ends. 



In D.indentm (Hall) the stipes generally exceed 1 inch (25*39 mm.) 

 in length, are parallel or subparallel, and have a uniform width 

 of about 2^ inch (1-05 mm.). The sicula is long, yL inch (2'53 mm.), 

 and the earliest developed theca appears to originate rather above 

 the sicula-base and to be closely adpressed to it. 



Yery few details regarding the thecae can be made out beyond 

 their number, which is about twenty-five in the space of 1 inch 

 (ten in 10 mm.). 



Occurrence. — Upper Skiddaw Slates and top of Middle Skiddaw 

 Slates. 



Localities. — Outerside ; Glenderamakin Eiver ; the Dodd, Skid- 

 daw ; Mosedale Beck, near Troutbeck. 



(h) DiDTMOGRAPTUS INDE^TTUS Var. NANUS, Lapw. 



1868. Didi/mograpstis geminus, Nicli. Quart. Journ. Geol. Soc. vol. xxiv, p. 134 

 & pi. V, figs. 8 & 9. 



1870. Didymograpsus geminus, Nich. Ann. Mag. Nat. Hist. ser. 4, vol. v, p. 346, 

 fig. 6. 



1875. DidymograpUis indentus var. nanus, Hopk. & Lapw. Quart. Journ. GeoL Soc. 

 vol. xxxi, p. 647, pi. xxxiii, fig. 7d & pi. xxxv, figs. 4a-c. 



The specimens now assigned to this species were originally referred 

 by Nicholson to D. geminus (His.), and he at the same time remarked 

 that D. indentus (Hall) was probably a large example of it. The 

 species in question is altogether different from Hisinger's, both in size 

 and increase of width, and also in other more minute particulars. 

 As Lapworth has pointed out, it is best considered as a dwarf variety 

 of D. indentus (Hall), with Avhich it agrees closely in everything 

 except size and the number of thecae in a given unit of length. 



The character of the proximal end agrees in all particulars with 

 D. indentus (Hall), but the stipes never exceed ^ inch (12*7 mm.) 

 in length, and are commonly narrower than in that species. 



The thecae seem to be far more numerous, being as many as 

 thirty to thirty-six in the inch (twel-?^ to fourteen in 10 mm.). 

 The apertures, so far as can be seen, seem to be perpendicular to 

 the general direction of the stipe. 



Occurrence. — On one slab from Outerside it is associated with 

 Tetragraptus serra (Brongn.). Middle and Upper Skiddaw Slates. 



Localities. — Outerside ; Glenderamakin Biver ; Thornship 

 Beck ; Barf ; Gatesgill ; Mosedale Beck, near Troutbeck. 



(6) DlDTMOGRAPTUS BIPIDTJS (Hall). 



1865. Graptolithus bifidus, Hall, ' Grapt. of the Quebec Group,' Geol. Surv. 

 Canada, dec. 2, p. 73, pi. i, figs. 16-18 & pi. iii, figs. 9 & 10. 



1868. Didymograpsus hifidus, Nich. Quart. Journ. Geol. Soc. vol. xxiv, p. 136. 



1870. Didymograpstis hifidus, Nich. Ann. Mag. Nat. Hist. ser. 4, vol. v, p. 346, 

 fig. 7. 



1875. Didymograptus hifidus, Hopk. & Lapw. Quart. Joui'n. Geol. Soc. vol. xxxi, 

 p. 646 & pi. xxxiii, figs. 8 a-e. 



Two forms of this species are known from the Skiddaw Slates : in 

 Q.J. G. S. No. 215. 2n 



