142 GENESIS OF THE AR1ETT1XE. 



this species. The abdominal view is not similar, not being flat enough on the 

 abdomen, but the lateral view has the straight perfect pike of this subseries. 



The Amm. Burgundice, Martin/ as identified at Semur, is identical with this 

 species. It is, however, smaller than those fron] Saulien, which are associated 

 with Psil. vlarwrbe, and is placed in the same bed as Liasicum. Wahner's figures 

 and description of Ariel. Sci/lla, 1 Reynes, seem to agree closely with the descrip- 

 tions and figures of this species. The aspect of the umbilical or young whorls 

 in Wahner's figures shows that Scylla, Wah., is certainly not identical with 

 the Johnsloni-like variety of Cal. raricostaium, though it very closely resembles 

 that form. 



Caloceras carusense. 



Plate I. Fig. 15, 16. Plate II. 1-3 a. Sumni. PI. XI. Fig. 15. 



Amm. carusensis, D'Okb., Terr. Jurass. Ceph., pi. Ixxxiv. fig. 3-6. 



Amm. Arietis, Ziet., Verst. Wiirt., p. 3, pi. ii. fig. 4 (not fig. 2, 3). 



Amm. spiratissimum, Hauer, Ceph. Lias Nordostl. Alpen, pi. iii. fig." 1-3. 2 



Amm. latisulcatus longicelta, Quenst., Amm. Schwab. Jura, pi. xii. fig. 5 (not fig. 1-4, 6). 



Amm. laqueus (pars), Quenst. 



Amm. Scylla (pars), Reynes, plates. 



Localities. — Lyme Regis, Semur, St. Thibault, Balingen, Willershausen in Hanover, Luxemburg. 



The characteristic of this species as given by D'Orbigny, the crossing of 

 the abdomen by the pilse, is not an important peculiarity, since it is com- 

 mon in the young of caloceran forms. The young of the normal variety is, 

 however, identical with D'Orbigny's figure. It acquires the keel when the 

 shell is about 25 mm. in diameter, and is at this stage very similar to one 

 variety of Cal. laqueum. The sides in the later stage and adults become more 

 flattened, and the abdomino-dorsal diameter of the whorl increases proportion- 

 ally. One variety in the Museum of Comparative Zoology has much stouter 

 more quadragonal whorls than this, with flattened sides and abdomen, though 

 the pilse are never very prominent or perfectly geniculated. 



The abdominal lobe is long, and much deeper than the superior laterals. 

 This is owing largely to the non-development of the superior laterals, which 

 remain short and broad. The superior lateral lobes are shallow and broad, the 

 inferior laterals narrow, and not usually long in proportion. The most character- 

 istic parts of the sutures are the first auxiliary saddles ; these are remarkably 

 large, and often tongue-shaped. The auxiliaries do not, therefore, incline back- 

 wards, at least in adults. The marginal lobes and saddles, and the margins of 

 the superior and inferior lateral saddles and lobes, are simple, and like those 

 of Psil. planorbe. 



This variety retains the keel until a very late age, even after the shell 

 becomes perfectly smooth. The form at this time is precisely similar to that 

 of the old of the stouter variety of Cal. Nodotianum or tortile ; subsequently, how- 

 ever, the whorl becomes round, as in Plate II. Fig. 1-3 a. This stout variety 



1 Mojsis. et Neum., Beitr., VI. pi. xxv. 



2 The specimen in Oppel's collection enabled me to quote this as a synonym. 



