﻿228 BRITISH FOSSIL CEPHALOPODA. 



to .24 of the diameter. The whorls are elongated in one direction, so that the general 

 contour is more elliptical than circular, and they are out of contact. No asymmetry 

 is observable. The section is rounded on the sides and flat on the front; but the 

 breadth is greater than the thickness, which may very well be due to compression. 

 The ribs, from 26-40 per whorl, are backward curving, acute, separate, dying away 

 into several deepish riblets on the front (fig. 4a), which meet in a rounded curve. 

 The body-chamber is more than half a whorl, and is continued for some distance in 

 a straight line. The septa are uniformly concave to the aperture, direct on the 

 whole, about ^ or less part of the whorl-breadth apart. One specimen shows trans- 

 verse epidermids. The only differences between our English specimens and the 

 Bohemian are that the section is not transverse in the former ; but none of the 

 specimens are uncompressed ; also that no longitudinal lines have been observed, 

 and the septa are a little wider apart. The remarkable proportions, the flatness 

 of the front, and the character of the ribs, including their dying off on the front, 

 are well exemplified. 



Relations. — The proportions of the whorls distinguish this from Trochoceras 

 rapax, to which it is allied by its ornaments and its whorls being out of contact. It 

 is doubtfully placed as a Lituites from its loose appearance. 



Distribution. — In the Lower Ludlow rocks of Ledbury (4). 



Lituites ibex, Sowerby, PI. XVIII. figs. 3, 4, 4a, 5. 



1838. Lituites ibex, Sowerby in Murchison's 'Silurian System,' pi. 11, fig. 6, p. 622. 



1852. Hoktolus ibex, M'Coy, ' Pal. Foss.' p. 324. 



1848. Orthoceras perelegans (part), Salter, 'Mem. Geol. Survey,' pt. 2, pi. 13, fig. 4 



(not figs. 2, 3). 

 1854. „ „ Salter in ' Siluria,' pi. 29, figs. 5, 6. 



1873. „ „ Salter, ' Camb. and Silurian Fossils,' p. 187. 



1873. Orthoceras tracheale, Salter, loc. cit., pp. 187, 192. 



Not 1838. Orthoceras ibex, Sowerby, loc. cit., pi. 5, fig. 30. 



Type. — Sowerby's type of Lituites ibex must not be confounded with his Ortho- 

 ceras of the same name, which he thought might belong to the same species, but 

 which is really different. I have not been able to discover the type, though Salter 

 appears to have done so, and to have identified it with his 0. perelegans. The 

 figure shows no section, and it may be circular. The curvature has at first a radius 

 of f of an inch only for the convex curve, but it soon diminishes to nearly zero. 

 The rate of increase measured as on a curved shell is i in 11. No characters of 

 body-chamber, aperture, septa, or siphuncle, are observable. The ornaments consist 

 of sharp transverse riblets, from \ to f the diameter apart, slightly oblique, curving 

 backwards to the convex side in the more coiled portion; they are non-separate, the 



