PLACENTICERATID®. 207 
separated from the young of P. bolli, although the tubercles of the inner line 
are less prominent at diameter of 45 mm., the volution being 23 mm. and 
greatest transverse diameter 11 mm. When the volution is 43 mm. from 
lines of involution to venter in same cast, the nodes in both lateral lines 
are very large and the ventral tubercles large, the ventral zone becoming 
sinuous on the cast in consequence of their size and arrangement. The 
venter also begins to show rotundity immediately after this, thus introducing 
the gerontic stage; the lateral zones begin to lose their flattened aspect, 
becoming more convex, the umbilical shoulders becoming correlatively 
rounded. The imner lines of nodes in this species are also apt to be elon- 
gated into ridges directed apically, as in polyopsis Dujardin. In the 
parephebic substage the volution from line of involution to venter in cast is 
41 mm., transverse diameter between nodes, which are not close to umbilical 
lines of involution, as in earlier stages, but about 14 mm. distant, is 26 mm., 
and through the nodes, which are probably somewhat worn down, it is 
30 mm. Ina more complete cast of 90 mm. in whole diameter, which has 
lost a trifle on the venter by weathering, the same rounding of the venter 
begins when the volution reaches about 32 mm. in ventro-dorsal diameter 
from lines of involution to venter. The nodes enlarge rapidly in the 
parephebic and gerontic stage of these two specimens, and fold-like cost 
appear which are obscurely bifurcated at the inner line of tubercles. The 
inner nodes are elongated, and have heavy, although not very prominent, 
folds on the umbilical zones which bend sharply apicad. The ventral zone 
gives place to a rounded area, as in the above, and the inner nodes are 
about 10 mm. distant from lines of involution instead of being only a few 
millimeters removed, as in earlier stages. They are, however, still on the 
umbilical shoulders, and, therefore, in same position as in the young with 
relation to the sides. 
Locality: Greene County?, Alabama. 
Age: Eutaw beds, Upper Cretaceous. 
PLACENTICERAS INTERCALARE Meek. 
Pls. XX XV-XXXVII; Pl. X XXVIII, fig. 1. 
Placenticeras placenta var. intercalare, Meek, 1876, Mon. U. S. Geol. Surv. Terr., 
Vol. IX, pl. 28. 
This was identified by Meek with placenta, but its characteristics were 
fully given by him and its relations to Ammonites syrtalis of Morton and 
