FOURTH, OR CORONICERAN BRANCH. 193 
pila, and shallow channels, show this plainly. They probably belong to the 
typical variety of Cor. Buckland, though the evidence must be considered incom- 
plete until the adults and young are known. 
Coroniceras orbiculatum, Hyarr. 
Coroniceras orbiculatum, Hyatt, Bull. Mus. Comp. Zodl., L., No. 5, p. 78. 
Amm. Bucklandi macer, Quenst., Amm. Schwib. Jura, pl. ix. fig. 2 (not fig. 1, 3); pl. x. fig. 5. 
Amm. Bucklandi costosus, QuENS?., Ibid., pl. x. fig. 1, 2. 
Amm. Bucklandi, QuENST., Ibid., pl. xi. fig. 2 (not fig. 1). 
Amm. oblongaries, QuENST., Ibid., pl. xiv. fig. 4. 
Localities. — Semur, Scheppenstadt, Balingen. 
The breadth and crowded aspect of the pilex in the Scheppenstadt specimen 
on the fourth and fifth whorl, and the narrowness of the sides, resemble the 
characteristics of the same age in Cor. Bucklandi, var. sinemuriense, more than any 
other species of the same genus. The young whorls are much too small in all 
their dimensions, and the volutions too numerous for Cor. Buckland. The adult, 
with its prominent tubercles and with the dorsal broader than the abdominal 
region, shows a remarkable resemblance to Cor. rotiforme. 
The last sutures on the ninth whorl have an even, rounded outline, due to 
the small size and regularity of the marginal lobes and the roundness of the mar- 
ginal saddles, which are similar to those of Cor. datum on the fifth volution. The 
abdominal lobe is about one half longer than the superior laterals, the inferior 
lateral saddles exceed the superior laterals by about two fifths. The saddles and 
lobes, however, are broad and comparatively short in Cor. datum and in the young 
of other forms of Coroniceras. One specimen which is identical with this in the 
septal outlines shows the abdominal lobe on the eighth whorl to be one third 
longer than the superior laterals, and the superior lateral saddles are not quite 
one third longer than the inferior laterals. 
One of the casts from Balingen measuring 288 mm. in diameter had about 
ten volutions. The increase in the transverse diameter of the whorl is more uni- 
form and gradual than in Cor. Bucklandi, var. sinemuriense. On the latter part of 
the ninth whorl the pile show the approach of old age in the loss of their tuber- 
cles. The genicule also descend farther upon the sides, and are less abruptly 
joined to the abdomen, which therefore is more rounded and prominent than in 
the adult. The channels have become shallower, and finally lose their lateral 
ridges upon the latter half of the tenth whorl. The keel is still of considerable 
size, and thus acquires somewhat greater prominence than in the preceding 
stages. The breadth of the abdomen measured across the geniculx is 6 mm. less 
than the breadth of the dorsum when measured through the umbilical shoulders 
on the second quarter of the tenth whorl, and 13 mm. less than on the fourth 
quarter of the same volution. 
The abdominal lobes were not visible on the last quarter of the ninth whorl, 
but the inferior lateral saddles were one sixth deeper than the superior laterals. 
On the second quarter of the tenth whorl the abdominal lobe was one half 
25 
