70 
NAUTILOIDEA. 
Horizon. Carboniferous Limestone. 
Locality. Ireland. 
Represented in the Collection by a single example. 
Subgenus TRIGOJNTOCERAS, M‘Coy L 
{Ortliocera, J. de C. Sowerby, 1825 2; Orihoceras^ Phillips, 1830^; 
Aploceras (pars), d’Orbigny, 1 849 ^ ; Cyrjtoceras, Giebel, 1852®; Cyrto- 
ceras, Barrande, 1867 ® ; Gyi’oceras, de Koninck, 1880 ; Cyrtoceras (sub- 
genus of), Blake, 1882®.) 
Suhgen. Char. Shell rapidly tapering, the apical part forming 
half a volution, the rest gently curving. The section is scutiform, 
Gyroceras {Trigonoceras) paradoxicum— a, lateral view ; b, front view, showing 
the strong dorsal keel ; c, ventral or peripheral view, showing its shallowly 
depressed surface, bounded on each side by two ridges. Some of the septa 
are here obscurely seen. Drawn from a specimen in the Collection. 
About one half natural size. 
^ Synopsis of the Carboniferous Fossils of Ireland, 1844, p. 6. 
2 Mineral Conchology, vol. v. p. 81. 
^ Geol. of Yorkshire, pt. ii. p. 239. 
^ Prodr. de Paleont. Stratigr, vol. i. p. 112. 
® Die Fauna der Yorwelt, Band 3, Abth i. p. 200. 
® Syst. Sil. du centre de la Boheme, vol. ii. pt. i. p. 448. 
Faune du Calc, Carbonifere de la Belgique (Anuales du Mus. Roy. d’Hist. 
Nat. de Belgique, tom. v.), p. 7. 
® British Foss. Ceph. pt. i. pp. 54, 56. 
