G en us — ORTH O C E R AS , B) 'eynius. 
OiiTHocEUAS STRIATUM, J. Sowcrby} 
PI. XXIV, Pig. 2. 
Ortliocera striata, J. Sowerby, 1814, Min. Conch., I, p. 129, pi. 58. 
Orttioceras striatum, P. McCoy, 1844, Synop. Carb. Poss. Ireland, p. 8 (non idem, P. 
McCoy, Brit. Pal. Poss., p. 405). 
A very large, straiglit, conical shell, with very thin longitnclinal ribs, 
partly interrupted and crossed transversely by more or less irregular, rather 
oblique, and sometimes slightly undulating lines of growth. The septa are 
concave, and suh^hemispherical, with horizontal margins. The siphuncle is 
central, rounded, rather funnel-shaped, and having nearly one-tenth of the 
diameter of the septa. The distance between the septa varies with the pro- 
gressive growth of the shell, so that the space between the last formed septa 
is eleven millimetres while ihat between the middle septa is only nine milli- 
metres. The last chamber is very long and spacious, seventeen centimetres 
long, with an oblique sharp edge, although its shell may he thicker for the 
length of two centimetres round the margin than on the rest of the shell. 
Dimensions. — As Mr. Clarke sent me an example of this species having 
an uninterrupted length of thirty-seven centimetres, and having its terminal 
chamber preserved, it was not difhcult to determine the total length of the 
shell when perfect. Its length would he about seventy-five centimetres, and 
the apical angle of its lower extremity about two and a half or three degrees, 
supposing that the lower and missiug part of the shell is as regular as the 
upper part which has served for this description. The diameter of the 
terminal aperture is about four and a half centimetres. 
Relations and Differences. — This beautiful species is easily distinguished 
from 0. cinctum, Sowerby, and 0. Morrisianuni, L. G. de Kouinck, which have 
their surfaces ornamented witli transverse strire, by its numerous longitudinal 
ribs, no traces of which are visible on the species just quoted. My O. lineale 
differs by having no lines of growth. There is also a decided difference in 
the apical angles of all these species, in the shape of their septa, and also in 
’ [Actinoceras striatum. J. Sowerby (?). A. H. Foord, Cat. Foss. Cephal. B. M. Nat. Hist., 1891, TI, p. ,SS2. 
Compare also R. Etheridge, Junr., Geol. and Pal. Q’laiicl., 1892, p. 293, t. 15, f. 1. — W.S.D.] 
