574 BRITISH PAL/EOZOIC FOSSILS. [CepHaLopopa, 
accidental. I have been obliged to give a new specific name to this species, as Phillips’s O. laterale proposed as 
a substitute (in consequence of Sowerby’s specific name having been previously used by Schlotheim) differs 
from the true species of Sowerby in having much more distant septa, and more nearly central siphon. To 
the present species may probably, however, be referred the O. imbricatum from Marwood, figured in Phillips’s 
Paleozoic Fossils, which is probably distinct from the Silurian one of that name. In the present shell specimens 
having the long diameter one inch seven lines, have eleven septa in that space, but the shorter diameter at the 
same point being only one inch five lines, there are only ten septa when compared with it; in most specimens, 
the mean between the long and short diameters will equal ten interseptal spaces throughout, at least down to 
a diameter of eight lines. There is a slight constriction near the anterior end of the last chamber. 
Position and Locality Not very uncommon in the carboniferous limestone of Lowick, Northumberland ; 
rare in the carboniferous limestone of Closeburn, Dumfriesshire. 
OrtTHOCERAS (Cycloceras) UNDATUM (Lfem.) 
Ref. and Syn.= O. undata Flem. Ann. Philos. Vol. V. t.31. f..7= 0. annulatum Phill. Geol. York. Vol. II. 
t. 21. f. 9,10 (not of Sow., subsequently O. Jineolatum Phill. Pal. Foss.) ;? = O. dactyliophorum de Kon. 
Anim. Foss. Bel. t. 47. f. 2. 
Dese.—Conoidal, rather rapidly tapering; section very broad-oval, nearly circular; septa very convex, 
distant; siphon of moderate size, almost exactly central, or less than half its diameter, eccentric towards the 
upper broad side. Surface marked with very slightly oblique, strong, prominent, rounded rings, with a faint 
sigmoid undulation on the sides; interannular spaces considerably broader than the rings; two interannular 
spaces, or two rings, between each pair of distant septa ; usually five interannular spaces in a space equal to the 
diameter (rarely half an interannular space, more or less) ; surface, when well preserved, marked with fine, sharp, 
transverse strie (nine or ten from the centre of one ridge to the next) ; the rings seem to become partially 
obsolete at the anterior end of old specimens of an inch and half in diameter. One specimen, two inches eleven 
lines long, and one inch six lines in diameter at anterior end, tapers regularly to seven and half lines in 
diameter at the smaller imperfect end; the proportion of the lateral to the antero-posterior diameters of the 
section are as one hundred to ninety. 
Most of the specimens seem smooth, as the Rev. Dr Fleming describes them, but when well preserved 
they are distinctly striated transversely, and all the smooth specimens manifestly want the external surface. 
Prof. Fleming alludes to an “ obscurely striated epidermis,” which may be a portion of the true surface, and it 
is just possible that his O. swlcata may belong to the same species, although it tapers more slowly than any 
thing I have seen of this type. 
Position and Locality.—Not very uncommon in the carboniferous limestone of Lowick, Northumberland ; 
rare in the black beds over the main carboniferous limestone of Derbyshire; not uncommon in the coal-shale 
near Glasgow. 
