﻿RHYNCHONELLA. 



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than was indicated by Professor M'Coy. We have already had occasion to remark that in 

 certain young shells of R. pleurodon a small portion of the beak and umbone was some- 

 times smooth, as is seen in the small R. triplex from Kildress. In the shales, on the upper 

 portion of the Carboniferous limestone at Settle, in the parish of Carluke, and elsewhere, 

 we find small specimens of a Rhynchonella with nine ribs, and which agree with the 

 characters assigned by M'Coy to his species ; but here also we observe that they pass, by 

 insensible gradation, into R. pleurodon, and in some the sinus and fold is unsymmetrical 

 or twisted, as was the case with the shell upon which Sowerby founded his Terebra- 

 tula Manila;. 



The specimen represented and described by General Portlock in pi. xxxviii, fig. 4, of 

 his excellent ' Report on the Geology of Londonderry, Tyrone, and Fermanagh,' as Tere- 

 bratula (?) ferita, (?), V. Buch, and which was found also in the red or yellow sandstone 

 of Kildress, is evidently a young example of R. pleurodon ; Von Buch's species being 

 quite distinct, and belonging to another genus (Relzia). 



It is well known, as I have already so often had occasion to remark, that the number 

 of ribs varies exceedingly according to age and specimen in almost every known species of 

 Rhynchonella, so that no definite number can be made use of as an unvariable character, 

 and no name given to a species should be founded upon the number of ribs possessed by 

 a single specimen. 



Loc. In England R. pleurodon is abundant in the Carboniferous limestones and 

 shales at Bolland, Settle, Kirby Lonsdale, Orton, and in several other Yorkshire and Derby- 

 shire localities, &c. In Scotland it is found in similar beds in various localities in Lanark- 

 shire, near Carluke, Campsie, also in Westlothian. In Ireland it occurs in the red sand- 

 stone of Kildress, and in the limestone and shales of other localities. It is also a common 

 fossil in other Carboniferous districts of the world. At Vise, in Belgium, by Professor De 

 Koninck. In Russia it is described from Archangleskoi, Cosatchi-datchi, Sterlitamak, &c. 

 In Australia it has been recently discovered in beds of the Carboniferous period at Bun- 

 daba, Port Stephen ; and is common in the Carboniferous rocks of America, &c. 



Rhynchonella flexistria, Phillips (sp.) PI. XXIV, figs. 1 — 8. 



Terebratula flexistria, Phillips. Geol. York., vol. ii, p. 222, pi. xii, figs, 33 and 34, 



1836. 



— tumida. Ibid., fig. 35. 



Hemithyris heteroplycha, M'Coy. Annals and Mag. of Nat. Hist., 2d series, vol. x, and 



British Palaeozoic Fossils, p. 440, pi. iii D, fig. 19, 1855. 



— flexistria. British Palaeozoic Fossils, p. 439. 



Spec. Char. Shell oblate, or transversely ovate ; dorsal valve more convex than the 



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