ORTHOCEIUTID^. 
51 
and the rate of increase is 1 in 12. There is no curvature what- 
ever. The ornaments are acute ribs, though rather rounded in the 
casts ; they are scarcely separate, are quite direct, and distant -J- to |- 
the diameter. When well preserved, there are sharp riblets parallel 
to the ribs, somewhat imbricating downwards. The septa are 
parallel to the ribs, and lie in the interspaces ; their convexity is 
ver}’ small, indeed they are remarkably flat. The siphunclo is 
small, and nearly central. {Blalce.) 
Remarlcs. This species closely resembles 0. ihex^ but it differs 
therefrom in the directness of its annulations. 
Horizon. Upper Ludlow (Downtonian). 
Locality. “ Brook Faim Lane.” (Xo further particulars about 
the locality of this fossil are obtainable. It was very probably 
collected in the neighbourhood of Ludlow, Shropshire.) 
Represented by one specimen presented by J. E. Lee, Esq., 
F.S.A., F.G.S. 
Orthoceras ibex, Sowerby. 
1839. Orthoceras ibex, Sowerby, inMurchison’s Sil. Syst. p. 613, pi. v. f. 30. 
1839. Orthoceras articulatnm, Sowerby, ibid. f. 31. 
1868. Orthoceras ibex. Dixon, Trans. Woolhope Naturalists’ Field Club, 
Fossil Sketches, Xo. 1, f. 2. 
1882. Orthoceras ibex, Blake, British Foss. Ceph. pt. i. p. 95, pi. v. 
ff. 3, 3 4, 5, 8. 
1839. Lituites ibex, Sowerby, in ^lurchison’s Si]. Syst. p. 622, 
pi. xi. f. 6. — 1852. Orthoceras {Cycloceras') ibex, M‘Coy, British 
Pal. Foss. p. 319 . — 1852. Orthoceras ibex, Salter, ibid. Appendix A, 
p. vii. — 1852. llortolus ibex, MUoy, British Pal. Foss. p. 324. — 
1873. OHhoceras ibex, Salter, Cat. Canibr. and Sil. Foss. p. 71.] 
Sp. Char. Section circular. The rate of increase is slow, but it 
cannot be accurately ascertained owing to the frequently compressed 
condition of the specimens. Septa not seen in the type, nor in any 
of the specimens in the National Collection. The body-chamber 
attains in some individuals a length equalling flvc times its basal 
diameter. The siphuncle is apparently a little eccentric. The 
surface is ornamented with rounded or subangular annulations, 
generally with a little obliquity, amounting in some specimens to 
10°. The distance of the ribs or annulations varies from L to | the 
longer diameter. The surface, when well preserved, is seen to be 
covered with numerous transverse lines, parallel to the annulations. 
The latter entirely disappear towards the aperture. 
Horizon. Wenlock Shales, Upper Ludlow (Salopian and Down- 
tonian). 
Localities. Benson Knot, Kendal, Westmoreland ', By ton Cross, 
E 2 
