SPIRIFERA. 37 



Obs. Many examples of this very variable species bear so great a general resemblance 

 to the Carboniferous Sp. ovalis, and to its transverse variety, Sp. hemispharica, M'Coy, 

 that I am in no way convinced we are justified while making use of a distinctive denomi- 

 nation for the Devonian shell. 



It has been urged that, in perfectly preserved examples of Sp. undifera, the surface is 

 regularly crossed by numerous concentric, contiguous striae or ridges, while in Sp. 

 ovalis the surface is smooth ; but it must likewise be borne in mind that we but very rarely 

 meet with any Carboniferous shells so perfectly preserved as to exhibit their delicate outer 

 surface, the larger number being decorticated ; and this is also the condition in which we 

 find almost all our British specimens of Sp. undifera. 



Having requested Messrs. Young and J. Thompson to kindly search for some well- 

 preserved examples of the Carboniferous Sp. ovalis, they were so fortunate as to find one 

 or two at Corrieburn and Brockley, in Scotland, in which the outer surface was closely 

 covered with numerous fine concentric striae or ridges, very nearly resembling those 

 observable in Sp. undifera. 



Sp. undifera is a common shell in the Middle Devonian limestone of Woolborough 

 Quarry, near Newton Abbot, and has been also found in that of Barton and Lummaton, 

 near Torquay. On the Continent it occurs in the Eifel, in Nassau, at Jerques, &c. 



Spirifera undifera, var. undulata, F. Roemer. PI. VIII, figs. 1 1 — 14. 



Spirifer curvatus, Schloth., var. undulatus, F. Roemer. Rheiniscb. Uebergangsgeb., 

 p. 70, pi. iv, fig. 5, 1844. 

 — undifer, Schnur, in Dunker's Paleeontographica, vol. iii, p. 204, pi. xxxiv, 

 fig. 9 ^ and *, 1853. 



Spec. Char. Shell transversely oval ; hinge-line shorter than the width of the shell ; 

 cardinal angles rounded ; dorsal valve convex ; mesial fold simple, wide, divided along the 

 middle by a shallow, longitudinal depression or groove, each valve being ornamented with 

 from twenty to thirty rounded or slightly angular ribs, of which (in some specimens) a certain 

 number are clue to the bifurcation or intercalation of additional ribs at variable distances 

 from the beaks. Ventral valve rather deeper than the opposite one, with a sinus of 

 variable width and depth, flattened along the middle, and with one or two feebly marked 

 ribs along its sides ; beak moderately produced and incurved ; area triangular, of moderate 

 size. Surface of the shell regularly crossed by numerous concentric ridges, as in the type 

 undifera. Proportions variable. 



Length 18, width 25, depth 14 lines. 



Obs. After very considerable hesitation and uncertainty, I have ventured to refer figures 

 11 to 14 of our plate to a well-marked variety or modification in shape of Sp. undifera, 

 and this notwithstanding the bifurcation and intercalation of some of the ribs, which is 



