70 DEVONIAN FAUNA. 



considerably smaller, but very fine, in the British Museum, and one in the Museum 

 of Practical Geology. 



Bemarhs. — It is to be regretted that, although the suture-lines are to be traced 

 through the transparent surface of the shell in several of our specimens, their 

 shape can only be made out, and that with the utmost difficulty, in a single case. 

 Mr. Foord and I, however, convinced ourselves that there was only one central and 

 one lateral lobe. The suture-lines approach each other at about two-thirds their 

 distance from the umbilicus, so as to form a kind of tangent curve. The curious 

 external markings appear to be due to the impression of the mantle. 



Affinities. — From the other Devonshire species it is easily distinguished by its 

 closed umbilicus, its flattened shape, and its very large size. Some of the Conti- 

 nental forms, however, approach it rather nearly in outward shape, although gene- 

 rally the character of the lobation proves the resemblance to be merely superficial. 

 G. ovatus,^ Miinster, has a broader back, less oblique sides, and a smaller and less 

 expanded mouth ; its umbilical depression is also less distinct. G. sublinearis, 

 Miinster,^ is a deeper and differently ornamented shell. G. linearis, Miinst.,^ is 

 still further separated from it by its depth, its broad and more flatly rounded back, 

 and its radiating lineations. G. Munsteri, von Buch,* has more evenly convex whorls, 

 a broader rounded back, an open umbilicus, and two lateral lobes in the suture- 

 line. G. subbilobatus, Miinster,^ is a deeper shell with a peculiar pinching-in at the 

 centre, and has broader chambers and a concave central saddle in the suture-line. 



G. bilanceolatus, Sandb.,'' is a much deeper shell, with two lateral lobes. (In his 

 plates Sandberger also gives the names G. Munsteri and G. bidens, but unites the 

 three in the text.) 



G. Bronni, Miinster, as given by Geinitz'' is more obliquely coiled, and has a 

 second lateral lobe in the suture. 



G. iiitumescens, Beyrich, as given by Tschernyschew,^ has a larger umbilicus 

 and a more angulated suture-line ; as given by F. Eomer,^ it has a still larger 

 umbilicus, a sharp keel, and angular lobes. G. simplex, von Buch,^" comes, according 

 to Tschernyschew,^^ much nearer, but has a much less undulated suture-line. The 

 latter species so nearly approaches it in other respects, that it is doubtful whether 

 it ought not to be regarded as a synonym. 



• 1832, Miinst., ' Uber Clym. und Gon. Pichtelgeb.,' p. 14, pi. ivA, figs. la—d. 



'^ Ibid., p. 17, pi. iv A, figs. 5 a — c. 3 ibid., p. 17, pi. v a, figs. 1 a — d. 



4 Ibid., p. 19, pi. V a, figs. 3 a—e ; and 1870, Tietze, ' Dev. Schicht. Ebersd.,' p. 28, pi. i, fig. 7. 



•^ 1839, Miinst.. 'Beitr.,' pt. 1, p. 21, pi. xvii, figs. la—c. 



" 1851, Sandb., ' Verst. Ehein. Nassau,' p. 71, pi. v, fig. 2 ; pi. viii, fig. 11, and pi. ix, fig. 7. 



7 1852, Geinitz, ' Verst. Grauw. Sachsen,' p. 39, pi. x, figs. 8—10 ; and pi. xi, fig. 2. 



« 1887, Tschernyschew, ' Mem. Com. Geol. Euss.,' vol. iii, pt. 3, p. 168, pi. ii, figs. 1, 3, 5. 



» 1876, Ferd. Eomer, ' Leth. Pal.,' pi. xxxv, fig. 10. 



10 1832, von Bucb, ' Uber Amm. und Gon.,' p. 42, pi. ii, fig. 8. 



11 1887, Tschernyschew, ' Mem. Com. Geol. Euss.,' vol. iii, pt. 3, p. 169, pi. ii, fig. 9. 



