PLATE I. 

 Geuus Didymograptus, M'Coy. 



FIGS. 



1 a, b. — Didymogyiijifus extensiis. Hall. 



1 a. Long specimen. Randal Crag. Skiddaw Slates. Woodwardian Museum, Cambridge. 



1 h. Fragment of stipe, badly preserv^ed. Figured, Hopkinson, Quai't. Joiim. Geol. Soc, 



1875, pi. xxxiii, fig. 1 a. Eoad Uchaf, Eamsej I. Lower Arenig (Hicks). Wood- 

 wardian Museum. 



2 a — c. — Didymograptus nitidvs, Hall. 



2 a. Long specimen and more reclined than usual. East of Longside. Skiddaw Slates. 



Woo<lwardian Museum. 

 2 h. Horizontal form. Randal Crag. Skiddaw Slates. Woodwardian Museum. 

 2 c. Broad form, more declined than usual. Outerside, Keswick. Skiddaw Slates. 



British Museum (Natural History), S. Kensington. 



3. — Didymograptus, cf . uniformis, Elles and Wood, sp. nov. 



Obverse view. Raulnay. Skiddaw Slates. Mr. Christopberson's Collection, Keswick. 



4. — Didymogrnptiis uniformis, Elles and Wood, sp. nov. 



Obverse view, well preserved, in relief. Bassenthwaite. Skiddaw Slates. Mr. Postle- 

 thwaite's Collection, Keswick. 



5 a — c. — Didymograptus hirundo. Salter. 



5 a. Obverse view, showing portion of intei'ior. From old wall near " Travellers' Rest," 

 Whinlatter. Skiddaw Slates. Mr. Postlethwaite's Collection. 



5 b. Reverse view, well-preserved specimen showing portions of interior. Randal Crag. 

 Skiddaw Slates. Woodwardian Museum. 



5 c. Badly preserved example. Type specimen. Figured by Salter in Quart. Journ. Geol. 



Soc, 1863, fig. 13/ EUergill. Skiddaw Slates. Museum of Practical Geology, 

 Jermyn Street. 



6 a, b. -Didymograptus sparsus, Hopk. 



6 a. Deformed specimen, jn-eserved in cleaved black shale. Type specimen. Figured, 



Hopkinson, Quart. Journ. Geol. Soc, 1875, j)l. xxxiii, fig. 2 a Road Uchaf, 

 Ramsey I. Arenig (Lower Arenig, Hicks). Woodwardian Museum. 

 6 b. Ibid., fig.' 2d. ' 



7. — Didymograptus pennatulus. Hall. 



Isolated stipe associated with D. sparsus. Ibid., fig. 3 e. 



8 a, — c. — Didymograptus patulus. Hall. 



8 a. Showing proximal extremity. Figured, Hopkinson, Quart. Journ. Geol. Soc, 1875, 

 pi. xxxiii, fig. 4 b. Porth-hayog, Ramsey I. Upper Arenig (Lower Llanvirn, Hicks). 

 Woodwardian Museum. 



8 b. Isolated and imperfect stipe. Ibid., fig. 4 a. Woodwardian Museum. 



8 c. Isolated stipe. Porth-hayog. Woodwardian Museum. 



9 a, b. — Didymograptus superstes, Lapw. 



9 a. Obverse view, well pi-eserved in black shale. Tvpe specimen. Figured, Lapworth, 



Proc. Belfast Nat Field Club (co. Down), pi vii, fig. 15 rt. Biruock, S. Scotland. 

 Gleukiln Shales. Professor Lapworth's Collection, Birmingham. 

 9 b. Distal portion of stipe. Ibid. 



10 a, b. — Didymograptus euodus, Lapw. 



10 a. Proximal extremity. Ty|ie specimen. Figured, Quart. Journ. Geol. Soc, 1875, 

 pi. XXXV, fig. 1 a. Abereiddy Bay. Llandeilo (Up. Llanvirn, Hicks). Wood- 

 wardian Mviseum. 



10 b. Distal pai-t of isolated stipe. Ibid., fig. 1 c. 



