METOICOCERATID ®. 119 
stage than figs. 14, 15, and the last node near the umbilicus on this was 
considerably larger than the preceding nodes, indicating that this young 
one belonged to this species. The breadth cf side at this age was about 
9 mm., the transverse diameter about 6 mm. The breadth of the side at 
the base of the living chamber, which was badly crushed farther on, in 
fig. 16 is 20 mm., while the diameter between the tubercles is 16 mm. The 
young volution was quadrate in form, the sides parallel, whereas in the 
specimen represented by fig. 16, as may be seen in fig. 17, the lateral zones 
are highly inclined and the venter much narrower than in the young. In 
the fossil shown on Pl. XII, fig. 2, the breadth of the side at the third suture 
is about 33 mm., the transverse diameter between the coste being 23 mm. 
The outward inclination of the sides in this specimen was not so great as in 
the fossil represented by Pl. XI, figs. 16, 17, even at the same stage, and 
the nodes near the umbilicus were apparently not quite so prominent. 
Besides the marked prominence of the nodes and their dichotomous costz, 
the living chamber in the young (figs. 14, 15) is clearly nearly three- 
fourths of a volution in length, while in the later stage it appears to be in 
part complete and to be one-half of a volutionin length. It is obvious that 
this species becomes more compressed with increasing age, and has a much 
narrower venter and less transverse diameter in proportion to the ventro- 
dorsal than in the young. The protoconch has an arcuate venter (Pl. XI, 
figs. 7-10) and rounded dorsum, with subangular bend as the outline 
approaches the opening of the conch. This opening, doubtless once the 
aperture of the protoconch, is much depressed or broad transversely and 
continues to have this form throughout the ananepionic and metanepionic 
substages. The elevation of the venter begins in the second volution, 
fig. 10, but the form remains smooth and the sutures goniatitic until 
about the fourth volution.* Then nodes begin to appear on the ventro- 
lateral angles and the venter becomes broader in consequence. The venter 
is smooth at this substage, the first of the neanic substages. In the next 
substage, about one-half of a volution later, fig. 14, the costee become more 
prominent near the umbilici and wrinkles appear on the venter, each 
accompanied by a pair of tubercles. In the next substage, which was not 
seen, it is probable that these ventral costze become connected with the 
lateral ones and equal in number to them, and nodes appear on the inner 
«This was guessed at. 
