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 pilae, 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 pilae 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 pila? than any specimens described above. On the second and third quarters 

 of the eleventh volution the pilce 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, Ziet., Verst. Wiirt., p. 18, pi. xiii, fig. 4. 



Amm. raricostatus, Quenst., Amm. Schwab. Jura, pi. xxiii. fig. 8-21, 24-31 ; pi. xxiv. fig. 1-3 (other figs., 



var. A). 

 Amm. raricostatus, Hauer, Ceph. Lias Novdostl. Alpen, pi. xvi. fig. 10-12. 

 Arid, raricostatus, Wright, Lias Amm., pi. xxvi. fig. 5-14 (pi. vii. fig. 2-6, var. A). 

 Ophioc. raricostatus, Hyatt, Bull. Mus. Comp. Zobl., I., No. 5, p. 75. 



The true pilse 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 pilae, the last of which 

 already begin to exhibit symptoms of senile degradation. On the eighth whorl 

 the pilse 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 Gal. tortile. 



The distinctions between this and the preceding variety are to be sought 

 in the sutures, the development of the pilas, and the size of the adult shell. 

 The young are precisely like the young of Gal. carusense, Amm. arietis, Ziet., 

 but on the fifth volution the whorl spreads out more laterally, and the pilae 



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