17-1 GENESIS OF THE ARIETID-E. 



Geyer, in his " Ceph. Hierlatz b. Hallstadt," gives figures and descriptions of 

 the following species of this genus. Am. (Psil.) abnorme and Snessi ; l Am. (Arid.) 

 semilevis, Plate III. Fig. 7, a channelled form like Am. cents ; Am. (Ariet.) ambigms, 

 and (Ariet.) of Quenstedt, Plate III. Fig. 14 ; the last is probably the same as 

 Am. cuneiforme, and probably the same as his undetermined species of Amphiceras 

 figured on Plate II. Fig. 30. Hauer, in his " Ceph. Lias Nordostl. Alpen," gives 

 figures and descriptions of Am. (Amm.) difformis, which may be the same as 

 semilevis, Geyer, though channels and keel are both figured as preceding the pilae 

 in his Plate VII. Fig. 12. His young specimen, Plate VII. Fig. 9, named Amm. 

 mutticostaius, is probably also a species of Arnioceras ; but the larger specimen, 

 Plate VII. Fig. 7, 8, is a coroniceran form. All of these were from Hierlatz. 



CORONICERAS. 



The young are stouter than in Caloceras or Arnioceras, and smooth for a 

 shorter period, and the stage following this usually has tuberculated pilae and a 

 whorl with more or less divergent sides. The abdomen in the adult is keeled and 

 channelled, the sides parallel or slightly convergent, the pila? being prominent and 

 heavily tuberculated. In the old, the tubercles are lost, the channels obsolete, 

 the keel very prominent, the abdomen very narrow, and the outline of the whorl 

 in section trigonal. 



The abdominal lobe in adults is deep and narrow, the superior lateral saddles 

 are generally shallower than the inferior laterals, and the first auxiliary lobes and 

 saddles are of comparatively small size. The great length of the abdominal lobe, 

 the shallowness of the superior lateral saddles, the small size of the first auxiliary 

 saddles, and the shortness and comparatively small size of their corresponding 

 superior and inferior lateral lobes, give great prominence to the inferior lateral 

 saddles. The outlines of the sutures are also much complicated, the marginal 

 lobes being broader and longer than is usual in this family. In old age the 

 abdominal lobe becomes shorter, often only slightly exceeding the superior 

 laterals in length. Degeneration also takes place in other lobes and saddles. 

 especially on the margins. The oldest sutures are, therefore, simpler than those 

 of the adult. 



The first subseries has heavily tuberculated pilae, and the whorl is very 

 gibbous near the umbilical shoulder. 



The second subseries has the tubercular and inner portions of the pilae more 

 nearly equal in prominence, the whorls are not usually so stout or numerous, and 

 the abdomen has a flatter outline. 



The third subseries is apt to have young with broader abdomens than in the 

 first two, and the pila? are frequently divided in the nealogic stages. Massive 

 whorls and pilae are characteristic of the first senile stage in the larger shells. 



1 Amm. Stiessi, Hauer, Unsym. Amm Hieilatz-Schichter, Sit/ Akad. Wien, 1S54. XIII. pi. i. fig. 1-6. 

 and the figures of Geyer, show that (his species has not, as supposed by Rolle, Sitz. Akad. Wien, 1857, 

 XX\ I , ami by Stur, Geol. d. Steirmark, any close affinity with Hagenowi from the Bone bed of the Wald- 

 bauser Hohe near Tubingen. 



