64 
simple, and nearly always equidistant, except on the ventral 
surface where they become rather closer, leaving very regular 
valleys between them, usually equal in width to that of three 
keels ; the whole of the keels and valleys are crossed by hue, 
regular, oblique, equidistant, continuous, longitudinal stride. 
Length (average) one and a half inches. 
Obs. — The spiral keels are remarkably regular, and simple in 
structure, at least twenty and perhaps more traversing the 
body whorl ; they retain their size as a rule, hut instances 
have occurred where they are alternately larger and smaller. 
The oblique transverse striae are uniform in size throughout 
their course, and do not in themselves enlarge on crossing the 
keels, hut the mere intersection of the two does give rise to a 
slight nodular appearance. The spaces thus enclosed between 
the two series of lines are oblong. 
It cannot be denied that both this shell and those usually 
referred to Cyclonema by authors, materially differ in appearance 
from Hall’s types of the genus. If a Cyclonema, it is a very 
large form, but at first sight it appeared to me referable to the 
allied genus Oriostoma, M. Chalmas, as defined by Hr. G. 
Lindstrom,* but the lengthened spire gives rise to a marked 
difference in the appearance of the two shells, nor does 
C. ? australis appear to have that laxity of coil seen in species 
of Oriostoma. 
C. ? australis is allied to the shell termed C . carinatum , var. 
multicarinatum , by Lindstrom,f but which I should have taken 
to be a species distinct from the other Gotland forms. Our 
species is a larger shell, with coarser and more numerous 
revolving keels on the whorls. The operculum should be 
sought for, as this will probably afford a means of accurately 
determining the genus. 
Genus Oriostoma, M. Chalmas , 1870. 
(Journ. Conch., Paris, xxiv., p. 103.) 
Oriostoma nortiii, sp. nov. 
(PI. ix., Figs. 6 and 7.) 
ftp. Char. — Shell discoid or ammonitif orm , biconcave, non- 
alate. ; back un symmetrically convex; spire very short, depressed 
below the plane of the body whorl ; whorls about six, all ex- 
posed ; body whorl generally convex on the upper surface, 
sloping downwards and inwards, bounded exteriorly by a 
strong spiral keel, from whence the surface gradually slopes 
away outwards to form the un symmetrical convex back ; the 
* Silurian Gastropoda and Pteropoda of Gotland (K. Svenska Vet. Akad 
Handling ar, 1884, xix.. No. 6), p. 156. 
f Loc. cit., p. 179, t. 18, f. 31-32. 
