170 GENESIS OF THE ARIETIDZ. 
Varieties B and C, from Semur, showed tubercular-like folds on the latter 
part of the first, and part of the second whorl, which were continued on the um- 
bilical border of the succeeding whorls, gradually developing into true pile on the 
third whorl. 
For a short interval in the specimen of variety A the shell is smooth again, 
and in that of variety C the folds still remain apparent, but so depressed that 
they were made out with difficulty. On the first quarter of the third whorl in 
one specimen of variety B, and the third quarter of a specimen of variety C, the 
folds reappear on the umbilical border, but develop so gradually that lateral pile 
are not produced until the latter part of the first quarter of the fourth whorl. 
Several other specimens of these same varieties, however, from the same locality, 
did not show the psiloceran folds in the young, or differ from those of variety A. 
A fragment from Ramert in the Museum of Stuttgardt is the true ceraliloides 
of Quenstedt, which differs from ceras in having a more prominent, narrower 
abdomen and shallower channels. 
A specimen of the stout variety from Cheltenham, named Bodleyi, Bruck., has 
well preserved young which show this species to be closely allied to ceras. The 
thinner variety described above has the young much compressed, and similar to 
the adult of the Cheltenham specimen. On the other hand, the young of the 
Cheltenham specimen is precisely like the adult of Arn. Hartmanni. Oppel’s de- 
scription shows that he identified the compressed variety as the Bodley: of Bruck., 
and the stout varieties as Amm. geometricus. 
Arnioceras falcaries, Hyarr. 
Plate Il. Fig. 25-27. 
Amm. falcaries, Quenst., Der Jura, p. 70, pl. vii. fig. 6 (not fig. 7). 
Amm. falcaries, QuENST., Amm. Schwab. Jura, pl. xiii. fig. 12-14. 
Arnioceras incipiens, Hyatt, Bull. Mus. Comp. Zool. I., No. 5, p. 74. 
Amm. acuticarinatus, Simps., Museum at Whitby? 
Amm. Youngi, Simps., Mon. Ammn., p. 46? 
Localities. —Semur, Robin Hood’s Bay, Balingen. 
The sides are convex, the whorls compressed, and the abdomen obtusely 
angular, keel prominent. ‘The pile begin with a line of tubercles, which appear 
on the first half of the fourth whorl, preceding the true pilze by about one fourth 
of a whorl. The pile are not strongly developed upon the umbilical shoulders 
of the whorls, which in many specimens are almost, smooth. 
Variety A, figured on Plate II. Fig. 25, 26, has prominent genicule and 
keel without channels, but some specimens leading to the next variety have less 
prominent genicule. 
Variety B has less prominent pile and keel. The channels, though mere 
linear depressions, begin to appear in some specimens. 
Variety C, figured on Plate H. Fig. 27, has even less prominent pilx, but a 
keel with distinct narrow channels, and in some specimens the pile were devel- 
oped abruptly, not being preceded by the usual line of tubercles. 
1 The ? in these cases is due to the fact that I was not permitted to examine the originals in the 
Museum at Whitby. 
