of 
404 BRITISH PALAXOZOIC FOSSILS. [CepHatopopa. 
CLYMENIA UNDULATA (Miinst.) 
Ref. and Syn. = Clymenia undulata + C. subleevis + C. inequistriata + C. sublinearis + C. linearis Minster, 
Ann. des Se. Nat. 2nd Series, Vol. II. t. 1. f. 6,7, 8, and t. 2. f. 1, 2 + Endosiphonites carinatus + E. 
minutus Ansted, Camb. Phil. Trans. Vol. VI. t. 8. f. 1, 2, 3. 
Sp. Ch.—Discoid, compressed, of about seven very gradually tapering whorls, almost entirely exposed ; 
whorls slightly convex on the sides, obtusely rounded on the periphery ; all the whorls crossed by fine, slightly 
unequal, sharp, slightly sigmoid strize, the umbilical ends of which are abruptly curved back, and those near the 
periphery abruptly curved forwards, forming on the periphery a deep rounded lobe, curved forwards; each side 
of the band formed by this lobe of the strize, often bounded by a very delicate thread-like keel, a similar keel 
often running along the middle, but all three easily effaced, /eaving the arched strie perfectly formed and un- 
injured beneath them ; sometimes every fifth or sixth of the strive stronger than the others; and where this 
occurs on the periphery, the intermediate ones are almost obsolete; above twelve strize in the space of one line 
under a strong lens; septa with the broad middle portion nearly direct, very slightly curved forwards ; first 
sinus very small, angular, projecting slightly in front of the margin of the middle portion; first lobe abruptly 
marked, angular, extending two-thirds the distance to the next septum, outer margins of this lobe in the various 
septa very slightly convex, following a line parallel with the periphery and umbilicus; inner margin convex near 
the apex of the lobe to half its height, then extending nearly direct to the edge of the umbilicus ; siphon large 
at the inner edge. Diameter of moderate sized specimen one inch four lines, proportional diameter of last 
whorl % to 4, width =. 
I imagined at first that our British species was distinct from the Clymenia linearis (Miinst.), to which it 
had been referred, by the strize on the periphery being of the same closeness as on the sides ; instead of the very 
remarkable appearance, figured and described by Minster, of the strive on the periphery being four or six times 
more distant than those on the sides, and forming a flattened band, limited by two thread-like keels. On 
examining a number of his original specimens, however, I find that although in parts the appearance he alludes 
to is very striking, yet with a good glass and a careful management of the light, fine stria, corresponding pre- 
cisely in number with those of the sides, may be traced between the stronger distant ones ; and other parts of 
the same specimens shew all the strize on the periphery and sides of equal size, strength, and number, in a.given 
space ; in parts again of some specimens the two fillets mentioned by Miinster may be seen, and even the third 
or mesial keel; while in other parts of the same specimen all three have disappeared, and the transverse strize 
pass without interruption across their site. I have, in short, satisfied myself that the supposed difference of all 
the above species cannot really be sustained even in different parts of the one specimen ; for certain of the strize 
occasionally become more prominent than the others, and the apparent flatness, or roundness of the periphery, 
depends upon the presence or absence of the lateral fillets, which I find to be as inconstant as the mesial keel. 
The keel seems to be the fowndation, so to speak, of the siphon, and the lateral fillets the foundation of the 
embracing edges of the coming whorl, indicating apparently a great extension of the shell-depositing organs, as 
in each case these ridges are superadded upon the already formed and perfectly sculptured whorls, from which 
they may be detached without injury. The convexity of the sides of the whorls varies slightly in the different 
specimens, and is rather greater in the inner than the outer whorls. The C. planorbiformis, which is united to 
the C. linearis by Professor Bronn, I find, on examining authentic specimens, to be perfectly distinct by the 
very great number, and gradual tapering of the whorls, and the small proportion which the last whorl bears to 
the entire diameter. 
Position and Locality —Common in the Deyonian limestone of S. Petherwin. 
Genus. CYRTOCERAS. See page 312. 
CYRTOCERAS? BDELLALITES (Phiil.) 
Ref.—Phill. Pal. Foss. f. 223. 
Sp. Ch.—Unciform, depressed ; siphon near the outer edges continuous, moniliform. 
