60 CARBONIFEROUS CKPHALOPODA OF IRELAND. 



Genus Strobocekas, Hi/att, 1883 (emend. 1893). 

 Gkoup op Stroboceras suloatum. 



a. Strobocbuas sulcatum,/, de G. Sowerhij, sp. Plate XX, figs. 10 — 12. 



1820. Nautilus sulcatus, /. de G. Sowerhy. Min. Couch., vol. vi, p. 1.37, 



pi. dlxxi, figs. 1 (cast), 2 (young). 

 1836. — —J. Phillips. Geology of Yorkshire, pt, 2, p. 233, 



pi. XX, figs. 81, 32. 

 ? 18i3. — — J. E. Portlock. Geology of Londonderry, p. 404. 



1844. — (DisciTEs) SULCATUS, F. M'Qoy. Synop. Carb. Foss. Ireland, 



p. 19, pi. iv, fig. 14 (fig. not quoted in the text). 

 ? 1860. DisciTES SULCATUS, iZ. Oriffith. Joum. Geol. S )c. Dublin, p. 561. 

 1891. — — A.R. Foord. Cat. Fos. Ceph British Museum, pt. 2, 



p. 95. 

 1893. Stroboceras sulcatum, A. Ryatt. Carboniferous Cephalopods. Second 



paper. Geological Survey of Texas, Fourth 

 Annual Report, 1892, p. 411. 

 [_Not 1844. Nautilus sulcatus, L. G. de Koninck. Desc. des Aniin. Foss. du Terr. 



Carbonifere de Belgique, p. 545, pi. xlvii, figs. 

 10 a, b; 1878, Fauiie du Calcaire Carbonifere 

 de la Belgique (Annales du Mus. Roy. d'Hist. 

 Nat. de Belgique, torn, ii), pt. 2, p. 126, pi. xx, 

 figs. 1—4.] 



Description. — Shell discoid, compressed, of a lenticular form, composed of two 

 and a half or three slightly embracing whorls, all of which are exposed in a 

 rather shallow umbilicus, which has a small central vacuity ; this is 4 mm. across 

 in a ventro-dorsally compressed shell, whose diameter is 45 mm. (PL XX, fig. 11). 



The apex or initial point is conical, and it is ornamented like the rest of the 

 shell, the three ridges which occupy the most prominent elevation on the sides 

 being developed upon it with proportional fineness. 



The whorl in section is broadly sagittate, the periphery very narrow, slightly 

 concave, and bordered by sharp keels. The sides are inflated in the lower two- 

 thirds, with three or four fine spiral ridges upon the most prominent part, tlie 

 lower keel forming the edge of the umbilicus. The upper third of the sides is 

 divided by a narrow projecting ridge into two deep sulci, which are not quite so 

 wide as the peripheral furrow. 



The body-chamber occupies about half of the last whorl. 



The septa are rather numerous, about twenty-six being contained in a complete 

 whorl. 



