FOURTH, OR CORONICERAN BRANCH. 193 



pilae, and shallow channels, show this plainly. They probably belong to the 

 typical variety of Cor. Bucklandi, though the evidence must be considered incom- 

 plete until the adults and young are known. 



Coroniceras orbiculatum, Hyatt. 



Coroniceras orbiculatum, Hyatt, Bull. Mus. Comp. Zool., L, No. 5, p. 78. 



Amm. Bucklandi macer, Quenst., Amm. Schwab. Jura, pi. ix. fig. 2 (not fig. 1, 3); pi. x. fig. 5. 



Amm. Bucklandi coslosus, Quenst., Ibid., pi. x. fig. 1, 2. 



Amm. Bucklandi, Quenst., Ibid., pi. xi. fig. 2 (not fig. 1). 



Amm. oblungaries, Quenst., Ibid., pi. xiv. fig. 4. 



Localities. — Semur, Scheppenstadt, Balingen. 



The breadth and crowded aspect of the pilae 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. Bucklandi 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. latum 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. latum 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 pilas show the approach of old age in the loss of their tuber- 

 cles. The genicular 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 genicular 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 



