174 GENESIS OF THE ARIETIDAL. 
Geyer, in his “ Ceph. Hierlatz b. Hallstadt,” gives figures and descriptions of 
the following species of this genus. Arn. (Psil.) abnorme and Suessi ;* Arn. ( Avie.) 
semilevis, Plate III. Fig. 7, a channelled form like Arn. ceras ; Arn. (Ariet.) ambiguus, 
and (Ariet.) of Quenstedt, Plate III. Fig. 14; the last is probably the same as 
Arn. cuneiforme, and probably the same as his undetermined species of Amphiceras 
figured on Plate II. Fig. 30. Hauer, in his “ Ceph. Lias Nordéstl. Alpen,” gives 
figures and descriptions of Arn. (Amm.) difformis, which may be the same as 
semilevis, Geyer, though channels and keel are both figured as preceding the pilee 
in his Plate VII. Fig. 12. His young specimen, Plate VII. Fig. 9, named Amm. 
multicostalus, 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 pile 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 piles 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 pile, and the whorl is very 
gibbous near the umbilical shoulder. 
The second subseries has the tubercular and inner portions of the pile 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 pile are characteristic of the first senile stage in the larger shells. 
1 Amm. Suessi, Hauer, Unsym. Amm. Hierlatz-Schichter, Sitz. Akad. Wien, 1854, XIII. pl. i. fig. 1-6, 
and the figures of Geyer, show that this species has not, as supposed by Rolle, Sitz. Akad. Wien, 1857, 
XXVL., and by Stur, Geol. d. Steirmark, any close affinity with Hagenowi from the Bone bed of the Wald- 
hauser Hohe near Tiibingen. 
