. Bulletin of the British Museum (Natural History), Geology. 268 R. A. FORTEY & R. M. OWENS. Fig. 121 Didymograptus (Expansograptus) sparsus Hopkinson 1875. a, near Arenig/Llanvirn bound- ary, Outerside, Cumbria, large undistorted specimen, x 1, Fitz Park Museum, Keswick, Harrison Coll.; b, Rhoad Uchaf, Ramsey Island, Dyfed, Fennian, probably B. rushtoni Biozone, slab with distorted material, x 3, SM A16951: pointer at centre bottom indicates inferred direction of extension. (Specimen at bottom is that used by Hopkinson (1875: pi. 33, fig. 3a) as illustrative of D. pennatulus,a\\ such spec
. Bulletin of the British Museum (Natural History), Geology. 268 R. A. FORTEY & R. M. OWENS. Fig. 121 Didymograptus (Expansograptus) sparsus Hopkinson 1875. a, near Arenig/Llanvirn bound- ary, Outerside, Cumbria, large undistorted specimen, x 1, Fitz Park Museum, Keswick, Harrison Coll.; b, Rhoad Uchaf, Ramsey Island, Dyfed, Fennian, probably B. rushtoni Biozone, slab with distorted material, x 3, SM A16951: pointer at centre bottom indicates inferred direction of extension. (Specimen at bottom is that used by Hopkinson (1875: pi. 33, fig. 3a) as illustrative of D. pennatulus,a\\ such specimens are here regarded as tectonically altered D. sparsus). Diagnosis. Large Expansograptus, proximal part declined, but only for two or three thecae, thereafter horizontal. Sicula large, stipes exceed 2 mm width at th 1 and achieve maximum width of about 2-8 mm (range of variation probably considerable) at about th 10, which then remains constant. Thecae very widely spaced, between 8 and 9 per 10 mm in mature part of stipe (th 10-th 15 5-5mm); apertures very flared, and deeply cut back to more than one-third stipe width, t = 1 mm, (p = 20°-30°. Discussion. The slab including the type specimen has obviously suffered a certain measure of distortion. The type specimen lies at a low oblique angle to the direction of maximum exten- sion, and the stipes have been slightly thinned as a result and the thecal spacing increased. Many of the other stipes on the type slab are close to the direction of extension: the very low thecal spacing recorded by Elles & Wood (1901) of 7 in 10 mm seems to be based on such specimens; on others preserved more or less normal to the long axis of the strain ellipsoid spacing is reduced to 10 or 11 in 10 mm. We regard almost all the specimens on the type slab as belonging to the single species sparsus, and include also a specimen from the same horizon figured by Hopkinson (1875: pi. 33, fig. 3a) as D. pennatulus Hall (which is one of the tectoni- ca
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