THIRD, OR VERMICERAN BRANCH. 145 
form of the whorl until about the sixth whorl. During this volution the 
abdominal region is raised to a slightly greater prominence, and the siphonal 
ridge appears. 
A large specimen from Semur shows pile, which are obtuse, but prominent 
and bent forward. These characteristics belong to the adult stage, and are 
preserved without change throughout the tenth whorl. On the ninth and tenth 
volutions the pil are very numerous, being respectively forty-one and _ thirty- 
eight in number, and the young of this shell must have had a larger number 
of pilx than any specimens described above. On the second and third quarters 
of the eleventh volution the pila became more and more depressed, and finally 
disappeared. The twelfth whorl was rounded and smooth, like that of the young, 
and therefore a good illustration of the nostologic stage. 
There is not usually much variation in the sutures of this species. The 
abdominal lobe is considerably longer than the superior lateral lobes, and the 
inferior laterals may be of about the same length, or not more than half as 
long. ‘The superior lateral lobes are broad at the summits and serrated, the 
inferior lateral lobes are very small in some specimens, owing to the small size 
of the first auxiliary saddles. The two larger saddles may be of equal depth, 
or the inferior laterals somewhat the deeper; the superior laterals are, however, 
very broad in proportion to their depth, and the inferior laterals much narrower, 
occasionally even club-shaped. These proportions are apparent at an early 
age, and were observed upon the latter part of the third whorl before the 
development of the marginal lobes. 
Var. B. 
Plate I. Fig. 24, 25 a 
Amm. raricostatus, Z1Ev., Verst. Wiirt., p. 18, pl. xiii, fig. 4. 
Amm. raricostatus, QuENST., Amm. Schwab. Jura, pl. xxiii. fig. 8-21, 24-31; pl. xxiv. fig. 1-8 (other figs., 
var. A). 
Amm. raricostatus, Haver, Ceph. Lias Nordostl. Alpen, pl. xvi. fig. 10-12. 
Ariet. raricostatus, Wrieut, Lias Amm., pl. xxvi. fig. 5-14 (pl. vii. fig. 2-6, var. A). 
Ophioc. raricostatus, Hyarr, Bull. Mus. Comp. Zodl., I., No. 5, p- 75. 
The true pile begin upon the third whorl. There are about forty on the 
third and fourth whorls, decreasing to about twenty-five on the fifth whorl, 
and on the seventh whorl there are only about twenty pile, the last of which 
already begin to exhibit symptoms of senile degradation. On the eighth whorl 
the pile are degraded to mere blunt folds, The remainder of this whorl could 
not be observed, but a fragment of the first quarter of the ninth shows that 
these blunted folds are still more depressed, being merely lateral ridges. The 
whorl at this time has an elevated abdomen, and the keel has disappeared. 
The form is similar to the old age of the stout variety of Cal. tortile. 
The distinctions between this and the preceding variety are to be sought 
in the sutures, the development of the pile, and the size of the adult shell. 
The young are precisely like the young of Cal. carusense, Amm. arictis, Ziet., 
but on the fifth volution the whorl spreads out more laterally, and the pilae 
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