28 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



two elements of difference between these species, viz. tbe rate of increase and 

 tbe width of the intervals between the sutures. 



This may be regarded as a very rare species, only one specimen having been 

 found in the course of several years of collecting. 



Remarks. — The group of forms to which Barrande 1 gave the name " Orthoceres 

 brevicones " are rare in the Carboniferous rocks. I am only acquainted with three 

 European species, viz. 0. dilatatum, de Kon., 2 0. cucullus, de Kon., 3 and 0. per- 

 conicum, Foord. The other Carboniferous species assigned by Barrande to the 

 brevicone group prove to be species of Poterioceras ; these are " Orthoceras" 

 cordiforme, J. Sow., and " 0." latissimum, Portl. The latter was even suggested 

 by its author to be " 0." cordiforme, its condition being too imperfect to admit of 

 certainty as to its true position. I shall have occasion to refer to this fragment 

 again later on. 



Family Actinoceratidji. 

 Genus Actinoceras, Bronn, 1837. 

 Acttnoceeas giganteum, J. Sowerby, sp. Plate IX, figs. 2 a — c. 



1821. Obthoceiu gigantea, J. Soioerby. Min. Conch., vol. iii, p. 81, pi. ecxlvi. 

 1836. Orthoceras giganteum, J. Phillips. Geo], of Yorkshire, pt. 2, p. 237, 



pi. xxi, fig. 3. 

 1840. Actinoceras Simmsii, C. Stokes. Trans. Geo!. Soc, ser. 2, vol. v, pt. 3, 



p. 708, pi. lis, figs. 4, 5. 



1843. — — J. F. Portlock. Eep. on the Geol. of Londonderry, 



&c, p. 391. 



1844. Orthoceras giganteum, L. G. de Koninck. Descrip. Anim. Foss. Belg., 



p. 510, pi. xliv, fig. 2; pi. xlv, fig. 3 ; pi. xlvi, 



and pi. xlvii, fig. 1. 

 1844. Actinoceuas giganteum, F. JSVGoy. Synop. Carb. Foss. Ireland, p. 11. 

 1844. — pyramidatum, F. M'Cuy. Ibid., p. 11, pi. i, fig. 5. 



1854. — giganteum, F. A. Roemer. Beitr. z. geol. Kenntn. des 



nordwest. Harzgeb., Palaeoutographica, Band 

 iii, p. 93, pi. xiii, figs. 27 a — c. 



1855. Orthoceras (Actinoceras) giganteum, F. 31'Coy. British Pal. Foss., 



fasc. 3, p. 571. 

 1862. Actinoceras giganteum, B. Griffith. Journ. Geol. Soc. Dublin, vol. ix, 



pp. 33 and 55. 

 1874. — — J. Young and J. Armstrong. Trans. Geol. Soc. 



Glasgow, vol. iv, p. 280. 



1 ' Syst. Sil. de la Bohcme,' vol. ii, p. 18. 



2 ' Descrip. Anim. Foss. Belg.,' 1842-4, p. 515, pi. xlv, figs. 8, 9. 



3 Idem, Suppl., 1851, p. 54, pi. lix, fig. 1. 



