FOURTH, OR CORONICERAN BRANCH. 167 
Arnioceras Hartmanni, Hyarr. 
Plate Il. Fig. 17, 18. Plate III. Fig.1, 1a. Summ. Pl. XII. Fig. 5. 
Amm. Harimanni, Oppr, Der Jura, p. 79; Wiirt. Jahresh., XII. p. 199. 
Amm. geometricus, OpPEL (pars), Ibid. 
Arn. kridiforme, Hyatt, Bull. Mus. Comp. Zodl., I., No. 5, p. 74. 
Amm. kridion, D’OrB., Terr, Jurass. Ceph., p. 205, pl. li. 3 
Amm. falcaries (pars), QuENST., Amm. Schwab. Jura, pl. xiii. fig. 21. 
Amm. robustus (pars), QUENST., Ibid., fig. 22. 
Localities. — Whitby, Lyme Regis, Semur, Bonnert, Suabia, Gmiind, Adnet. 
This species has more compressed adult whorls than any variety of Arn. semi- 
costatum, and, although the pile are similar, they begin to appear at an earlier 
age and are developed more gradually. The abdomen is also in many speci- 
mens, though not in all, distinctly channelled, and the keel prominent. 
In one’specimen the superior lateral lobes are nearly as long as the abdominal 
lobe on the sixth whorl, and on the sdme whorl in another they were two fifths 
shorter. The inferior lateral saddles are deeper than the superior laterals, and 
the inferior lateral lobes very short. 
A specimen in the Museum of Stuttgardt, collected by Prof. Fraas, is from 
Arietenkalk, Hechingen (No. 5026 of that collection); another, from Gmiind, 
was found in the Geometricus bed, and is labelled Amm. Nodotianus, D’Orb. Two 
others, from Behla, are labelled Amm. falcaries, Quenst.; these belong to his 
sparsely ribbed variety, which is just intermediate between Arn. Hartmanni, and 
some varieties of Arn. semicostatum. 
A specimen of falcaries, Quenstedt, figured by him,’ is described as partly 
unrolled. Examination of the broken end, however, shows that a calcareous 
worm tube has occasioned the distortion by having been built upon the abdomen 
of the growing shell. This is a common occurrence, and was observed in several 
specimens at Semur. There are others, however, in which this distortion, as in 
other species of Ammoniting, takes place without the presence of any foreign 
body between the whorls. Such examples have been named Crioceras Eryon and 
Mandubwis by Reynés. These and other cases show the kind of error likely to 
occur from the use of such names as Crioceras, Gyroceras, ete. 
The flattened sides and general aspect of Quenstedt’s figure of falcaries ro- 
bustus? agrees apparently more nearly with this species than any other known 
to me. This species is the one commonly named Amm. geometricus, Oppel, in 
the collections in Germany, and seems to have been in part confused with that 
species by Oppel. 
1 Der Jura, pl. viii. fig. 6. 2 Amm., Schwab. Jura. 
