. Bulletin of the British Museum (Natural History), Geology. ARENIG IN SOUTH WALES 269 3. th 10 20 30 40 50 Fig. 123 Stipe expansion diagrams for D. (Expansograptus) sparsus Hopkinson; a, wide stipe (called pennatulus by Hopkinson) from type locality; b, from holotype, technically extended (Elles & Wood 1901: pi. 1, fig. 6a); c, undistorted specimen Fig. 121a herein, lying about midway between these two extremes. Knowledge of D. sparsus in an undistorted condition has derived from a specimen from the Lake District, figured here as Fig. 121a. The specimen has a final stipe width of 2-8 mm,
. Bulletin of the British Museum (Natural History), Geology. ARENIG IN SOUTH WALES 269 3. th 10 20 30 40 50 Fig. 123 Stipe expansion diagrams for D. (Expansograptus) sparsus Hopkinson; a, wide stipe (called pennatulus by Hopkinson) from type locality; b, from holotype, technically extended (Elles & Wood 1901: pi. 1, fig. 6a); c, undistorted specimen Fig. 121a herein, lying about midway between these two extremes. Knowledge of D. sparsus in an undistorted condition has derived from a specimen from the Lake District, figured here as Fig. 121a. The specimen has a final stipe width of 2-8 mm, and its stipe expansion diagram lies between the wider and narrower specimens on the type slab (Fig. 123). The distal thecal spacing is between 8 and 9 thecae in 10 mm, which is still low for an Expansograptus. It is not possible to be sure exactly how much distortion accounts for the variation in distal stipe width on the type slab. Extreme values are 2-2 mm parallel to extension and just over 4 mm normal to it. The type specimen, 2-5 mm wide, is nearly parallel to exten- sion, and certainly thinned by tectonism. On the other hand some specimens nearly parallel to extension are 3 mm wide, and were originally wider. There was presumably a good deal of variation in final stipe width (as in other extensiforms), embracing the values 2-6 to 3-3 mm and maybe more. Taking the extreme values produced by distortion on the type slabs the formula original width = ^/compressed width x extended width gives values close to that of the Outerside specimen. The important specific character is not the stipe width, but the widely-spaced thecae with their flared apertures, and the wide initial stipe width with relatively low stipe expansion (Fig. 123). The species certainly grew very large: the Lake District specimen has one stipe 12 cm long without a termination. The proximal end of the holotype was figured by Elles & Wood; the sicula exceeds 3mm in length, but has possibly been tectonically
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