CEPHALOPODA. | LOWER PAL/ZOZOIC MOLLUSCA. 315 
ORTHOCERAS IMBRICATUM ( Wahl.) 
Ref —His. Leth. Suec. t. 9. f. 9. (siphon too near the edge) ; Sil. Syst. t. 9. f. 2. 
Sp. Ch.—Section broad-oval, very slowly tapering (from a diameter of one inch three lines tapers one and 
half lines in two inches) ; septa slightly oblique, with a shallow sigmoidal curve on the sides, and a shallow 
rounded wave on the dorsal and ventral aspects, the last ten or twelve septa (at a diameter of about an inch 
and a quarter) varying from one line to nearly a line and half apart; siphon rather large, about half its 
diameter from the centre towards the upper side. 
In Hisinger’s figure the siphon is erroneously represented close to the margin, but our specimen agrees 
with his description in having it subcentral; the dorsal wave of the septa is more curved in that figure than in 
our examples. 
Position and Locality —In the green Upper Ludlow quartzite of Kirkby Moor, Kendal, Westmoreland. 
ORTHOCERAS LAQUEATUM (fall). 
Ref—Hall, Pal. New York, t. 56. f. 1. 
Sp. Ch.—Tube slender, tapering at the rate of one line in one inch, from a diameter of five lines, at which 
size the septa are one line apart, direct, moderately convex ; siphon cylindrical, central; surface covered with 
sharp, rigid, equal, longitudinal, elevated lines, separated by wide concave spaces, about four in the space of one 
line, with or without one or more fine intermediate strice. 
This is easily distinguished from the O. filoswm or O. angulatum, by its more gradually tapering form and 
much finer lineation. The O. swbcostatum (Port.) is figured with fewer and more distant ridges, but seems 
very closely allied. 
Position and Locality—Upper Ludlow rock of Kirkby Moor, Kendal, Westmoreland; Upper Bala flags 
of Coldwell, Westmoreland ; schists of Dinas Bran, Llangollen, Denbighshire ; in flags on road from Coniston 
to Hawkshead, Lancashire. 
ORTHOCERAS LUDENSE (Sov.) 
Ref. and Syn.—Sil. Syst. t. 9. f..1. ¢= O. distans Sow. Sil. Syst. t. 8. f. 17. 
Sp. Ch.—Tapering at the rate of one line in one inch, almost uniformly from a diameter of three inches 
three lines; a specimen of that size at the perfect mouth, and one foot three inches long, is one inch six lines 
in diameter at the broken smaller end ; the straight septa throughout between these diameters having a distance 
of about seven lines apart; section almost circular; siphon large, very slightly eccentric ; surface with a few 
obtuse, obscure, transverse ridges towards the mouth. 
The large specimens are very instructive from demonstrating the uniform distance of the septa in a 
tube varying so greatly in diameter, rendering it probable that the O. distans may be the same species, 
as I have noticed nearly as great an eccentricity of siphon in some specimens of the ordinary character of 
O. Ludense. 
Position and Locality —Common in the Lower Ludlow rock of Green Quarry, Leintwardine, Shropshire. 
ORTHOCERAS (Actinoceras) MocKTREENSE (Soi.) 
Ref—Sow. Sil. Syst. t. 6. f. 11. 
Sp. Ch.—Elongate, conic, tapering at the rate of one line in one inch from a diameter of one inch 
four lines, at which size the slightly eccentric siphon is three lines in diameter and spherically inflated between 
the septa, which with the siphonal constrictions are there three lines apart, and moderately convex ; (surface 
nearly smooth, with irregular transverse lines of growth ?). 
This species differs from O, Brightii (Sow.), with which it is said (in the Memoirs of the Geol. Survey) 
that Mr Salter had identified it, by the tube tapering much more slowly, having a considerably smaller siphon, 
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