SPIRIFERA. 39 



mesial fold, while in some specimens the number is two on each side. The ribs on the 

 lateral portions of the valves are also more or less sharply defined in different specimens. 



After comparing the original examples of Sowerby's Sp. nuda with those of the same 

 author's, Sp. pulchella (Sowerby's types being preserved in the Museum of the Geological 

 Society), I arrived at the conclusion that the last-named shell is only a small variety or 

 condition of the first. In Sowerby's two examples which Ave have figured (23, 24) it will 

 be seen that the same disposition of ribs as described for Sp. nuda may be observed in 

 Sp. pidchella. We must not omit to call attention to the great similarity of character 

 existing between the Middle Devonian species and the Carboniferous Sp. triradialis (vol. 

 ii, p. 49, pi ix, figs. 4 — 12), the same disposition of ribs being prevalent; but the 

 Carboniferous shell is usually less transverse, and its beak smaller and more incurved. 



Spirifera nuda and its variety Sp. pulchella occur in the Middle Devonian limestone of 

 Dockyard, near Plymouth. It is found also at Woolborough, near Newton Abbot, at 

 Barton, and Lummaton, near Torquay, and at Dartington, near Totness, in Devonshire. 



Spirifera curvata, Schloth. (sp.). PL IV, figs. 29—32, 33 (?), 34 (?) ; PI. IX, figs. 26, 27. 



Terebratulites curvatus, Sehlotheim. Nacbtragen zur Petrefactenkunde, pi. xix, fig. 2, 



1822. 

 Spirifer curvatus, Buck. Ueber Delthyris, p. 52, 1837. 

 Delthyris — Gold/, in Von. Dechen's Handb., p. 526. 



Spirifer — Schnur. Uebergangsgebirge der Eifel, Bracbiopoden, in Dunker's 



Palaeontographica, iii, p. 208, pi. xxxvi, fig. 3. 



Spec. Char. Shell variable in shape, transversely oval, and usually wider than long ; 

 valves almost equally convex, with a mesial fold of variable elevation in the ventral valve, 

 to which corresponds a sinus in the opposite one ; hinge-line shorter than the width of 

 the shell ; cardinal angles rounded ; beak incurved ; ventral area triangular ; dorsal one 

 linear ; fissure partly covered over by a pseudo-deltidium ; surface closely crossed by rows 

 of imbricated, serrated ridges. Proportions very variable ; two specimens have measured — 



Length 19, width 24, depth 13 lines. 

 15, „ 16, „ 16 „ 



Obs. In general shape, the larger number of our British specimens of Sp. curvala are 

 undistinguishable from Sp. glabra; and, indeed, had we only the decorticate examples usually 

 met with in our Middle Devonian rocks (PI. IV, figs. 29 — 32), we should at once identify 

 them with Martin's Carboniferous shell. The difference, as far as we can at present 

 perceive, appears to rest in the external surface or sculpture; for in well-preserved 

 examples of Sp. curvata the shell is finely striated and closely imbricated, and decussated 

 by numerous transverse or concentric, finely serrated ridges (PI. IX, figs. 26, 27), 

 similar in character to those which may be seen in Sp. bisulcata, Sp. undifera, Sp. lineata, 



