110 DEVONIAN FAUNA. 



Affinities. — This species so mucTi resembles Cyrtoceras deci]jiens, Barrande,' 

 that I have been in some doubt about separating it from that species. The 

 differences to be noted are that the English shell is rather more arched and is 

 inequilateral and that the dorso-ventral diameter of the section is not so much 

 greater than the transverse section as it is in Barrande's fossil. The surface 

 markings also, which are similar (including the ventral sinus), do not seem so 

 strong. The larger "Wolborough specimen is decidedly more arched than is 

 Barrande's shell. Cyrtoceras intermedium^ Barrande, is another very similar 

 species, which, however, differs in the minor character of its ornament and 

 looks more like G. decipiens, Barr., than do any of our fossils. G. sporadictmi, 

 Barrande,^ differs from ours in having simple, equal transverse lines. Though 

 coming very close to all these three species, I consider that the present must 

 be regarded distinct from them on account of the obscurity and indistinctness 

 of its markings. C. distentum, Barrande,* nearly approaches it in general shape, 

 but the markings are not so equal, and the section is more regularly elliptic. 



Gomphoceras Verneuiliy Barr.,^ is also very like, but is decidedly more elongate ; 

 and G. mumia, Barr.,*' has a straight dorsal profile and coarser ornamentation. 



Gyrtoceras negatum, Barrande,'' appears to be a less elongate and more sym- 

 metrical form. Gyrtoceras parvulum^ Barrande,^ presents a very close resemblance 

 in its ornamentation, but it is a more arched shell, and never shows any signs 

 of asymmetry. 



G. memorator, Barrande,' seems at first sight so similar as to raise a question 

 of possible identity, but it presents important differences, — the sinus in the 

 ornamentation is on the concave instead of the convex side, there is no asymmetry, 

 and the transverse ornament is crossed by still finer and more numerous radiating 

 lines. 



^ 1865, Barrande, ' Syst. Sil.,' vol. ii, p. 544, pi. cxlvii, figs. 30—38, and pi. cliv, figs. 25—33, 

 fit. E. 



2 Ibid., p. 552, pi. cxlvii, figs. 27—29 ; pi. cxlix, figs. 13—17 ; pi. cl, figs. 1—27 ; pi. cli, figs. 22 

 —27, Et. E. 



a Ibid., p. 567, pi. cli, figs. 17—21, and pi. ccv, figs. 11, 12, tt. F. 



* Ibid., p. 546, pi. cxiv, figs. 1—7, Et. F. 



•' Ibid., p. 330, pi. Ixxi, figs. 1—9, Et. E. 



6 Ibid., p. 292, pi. Ixx, figs. 10—13 ; pi. xcii, figs. 4—7, Et. E. 



7 1866, ibid., p. 705, pi. cxlv, figs. 14, 15, and 1877, ibid., Suppt., p. 168, pl. cccclxvi, figs. 7, 8, 

 Et. G. 



** Ibid., p. 689, pl. clxxvii, figs. 12 — 18, and 1877, ibid., Suppt., pp. 39 and 169, pl. cccclxxxi, 

 figs. 1—15, and pl. div, figs. 1—45, Et. E. 



9 1877, ibid., Suppt., p. 158, pl. dxvi,figs. 8—11, Et. F. 



