60 CARBONIFEROUS CKPHALOPODA OF IRELAND. 



Geuiiti Stkoboceuas, Hi/atf, 1883 (emend. 1893). 

 Gi;ouP OF Sthobockras sulcatum. 



a. Strobockuas sulcatum,/, de G. Sowerhi/, sp. Plate XX, figs. 10 — 12. 



182G. Nautilus sulcatus, J. de O. Sowerbif. Min. Couch., vol. vi, p. 1.S7, 



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

 j^36. — — J. Phillips. Geology of Yorkshire, pt. 2, p. 233, 



pi. XX, figs. 31, 32. 

 r* 1843. — — J. E. Portlock. Geology of Londonderry, p. 404. 



1^44. — (DisciTEs) 8ULCATU8, F. M'Coy. Synop. Carb. Foss. IrelatiH, 



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

 ?1S60. DisccTES SULCATUS, i2. OriJiUi. J.)iiru. Geol. S )e. Dublin, p. 561. 

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



p. 95. 

 1893. Strohoceras sulcatum, A. Ri/att. Carboniferous Cephalopods. Second 



paper. Geological Survey of Texas, Fourth 

 Annual Report, 1892, p. 411. 

 [xVo? 1844. Nautilus sulcatus, L. G. de Koniiick. He^c. des Auiin. Foss. du Terr. 



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

 10 a, h ; 1878, Fautie du Calcaire Carbouifere 

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

 Niit. de Belgique, toni. ii), jit. 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 uinbiiicus, which has a small central vacuity ; this is 4 mm. across 

 in a ventro-dorsally compressed shell, whose diameter is 45 mm. (PI. 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 liy sharp keels. The sides are inflated in the lower two- 

 thirds, with three or four fine spiral rid^'es upon the most prominent part, the 

 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. 



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



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

 whorl. 



