570 BRITISH PALAZOZOIC FOSSILS. [CepHaLopopa. 
level on the inner, or concave, side of the general curve, and advanced correspondingly forwards on the dorsal, 
or convex, side; septa, in the greater part of the length, about a line and a half apart; the penultimate 
chamber, as usual, being smaller than the rest, and the septa only a line apart when the diameter is reduced 
to half an inch, and increasing to two lines apart when the diameter is one inch; transverse section broad- 
oval; siphon a little eccentric towards the inner or most posterior edge of the septa. Surface of the shell 
moderately thick, marked with fine transverse impressed strize, nearly parallel with the septa in direction, 
separated by flat spaces (about four in the space of one line). Average length of last chamber one inch two 
lines, lateral diameter of ditto at base one inch four and half lines ; antero-posterior diameter at mouth ten 
lines. A specimen with the above dimensions has the chambered portion four lines in lateral diameter at three 
inches from the base of the last chamber, and very slightly less in antero-posterior diameter. 
This very elegant species can only be confounded with the rare O. (Poterioceras) ventricosum (M°Coy), 
from which it is distinguished by its much more slender proportions. The last chamber is very commonly 
found apart, and owing to the sudden inward sloping of the ventral surface, the position of the siphon might 
very easily be mistaken, as what is really the concave face of the general curvature seems, in such a fragment, to 
be the exterior or convex side of the curve. The siphon is dilated between the chambers into spherical beads. 
Position and Locality.—Not very uncommon in the carboniferous limestone of Lowick, Northumberland ; 
yare in the red carboniferous limestone of Breedon, Leicestershire. 
OrtTHOcERAS (Campyloceras) GusNERL (Mart. Sp.) 
Ref, and Syn. = Conch. N. Orthoceras Gesnert Martin, Pet. Derb. t. 38. f. 1; de Kon. Anim. Foss. Bel t. 47. 
f. 4; (2) ineurved young, Mart. ib. f. 2; = O. Gesnert (Mart.) Phill. Geol. York. Vol. IJ. t.21.f. 6; = Cyrtoceras 
Gesneri de Kon. Anim. Foss. Bel. t. 60. f. 5; = C. tuberculatum M'Coy, Synop. t. 4. f. 2. 
Desc.—Very elongate, conic, very gradually tapering (at about an angle of 7°) (‘slightly arched in the young 
state towards the posterior end) ; surface with from twenty-two to thirty-six strong, equal, regular, narrow, pro- 
minent ridges, regularly tuberculated, and separated by smooth, slightly concave spaces, averaging twice the 
width of the ridges (a little less in young, a little more in old stages of growth). Septa simple, moderately 
numerous ; the penultimate and ante-penultimate little more than half the size of the preceding chambers ; 
section nearly circular, most so in young specimens, very broad-oval, in old ones; siphon about twice its 
diameter from the edge in young specimens, and slightly more in old ones. A specimen, imperfect at each end, 
three and half inches long, and one inch eight and half lines in diameter at the large end, tapers to one inch 
four and half lines at the smaller; the septa average two lines apart, except the two preceding the last 
chamber, which are only one line apart. 
There is much difference of opinion among authors as to whether the small slightly arched specimen 
figured by Martin (fig. 2) is the same species, or not, as his larger shell (fig. 1). M.de Koninck separates 
them generically; and | should at one time have done the same, but observing that the only difference 
between them is a slight curvature of the smaller ones, and the siphon of such specimens being very slightly 
nearer to the edge, I am led to the ccnclusion that the small specimens are merely the incurved posterior ends 
of the larger straight examples (somewhat as in the O. wnguis), and the slight difference in the position of the 
siphon would probably admit of the same explanation, as we know that the siphon of Nautilus imperialis and 
others is marginal in the young, and gradually becomes nearly central with age; the difference in number of 
ridges which I have mentioned above is independent of the size or other characters of the specimens. Since 
examining Derbyshire specimens of this species I perceive that Martin and Phillips have omitted the tuber- 
culation which really exists on the fine ridges; and as my C. tuberculatum was founded on the presence of this 
character, it must now merge into the old species of Martin, as has been already recognized by M. de 
Koninck in his supplement. 
Position and Locality.—Rare in the black marble beds of Derbyshire; rare in the carboniferous limestone 
of Kendal, Westmoreland ; and in the carboniferous limestone of Poolwash, Isle of Man. 
