PLACENTICERATID A. 237 
PLACENTICERAS DEPRESSUM n. sp. Hyatt. 
Placenticeras syrtale Grossouvre (pars), 1893, Ammonites Craie supérieure, p. 128, 
pl. 6, fig. 2 only, and pl. 7, fig. 1. 
Ammonites syrtalis Schliiter (pars), 1871, Paleontogr., Vol. XXI, pl. 14, figs. 9 and 
10 only. 
This French and German species is undoubtedly a very close ally of 
guadalupe and is called variety guadalupe by both authors, who suppose it 
to be identical with the American species of the same name. The latter, 
however, has not the costz in the young shown in the umbilicus as figured 
by Grossouvre on pl. 7, and the inner nodes in the American form are on 
the umbilical shoulder at all stages, the umbilici being deeper and the 
volution thicker or stouter in proportion This species also includes 
Grossouvre’s variety quadratum. The saddles are more deeply wndereut 
and outlines of both lobes and saddles more complex. They are, however, 
very closely representative species. Schliiter’s figure shows the impression 
of a keel in the impressed zone of the fragment of an outer volution, but 
this is probably either accidental or a mistake in the figure, judging from 
the description. The obvious excellence of Grossouyre’s work and figures 
enables one to see clearly the relations of these forms, and he describes 
them as varieties. We differ simply in our estimate of their relative impor- 
tance, he preferring to call them varieties, and I to name them as distinct 
species in accordance with the methods adopted in this and other papers. 
Age: Lower Senonian (Santonian). 
PLACENTICERAS GROSSOUVREI n. sp. Hyatt. 
Placenticeras syrtale (pars) Grossouvre, 1893, Ammonites Craie supérieure, pl. 5, 
fig. 32; p. 16, fig. 1 (no others). 
The French form has no corresponding representative now known m 
this country. The young, if it be the young, figured on pl. 5, is costated 
like the gerontic stage of polyopsis of Dujardin, but it also has a prominent, 
closely set row of tubercles on either side of the narrow concave venter, 
The large fossil figured on pl. 6 has an umbilicus so very different that if 
it belonged to almost any other genus one would say at once it could not 
be the same. In this genus, however, the young are so compressed and 
distinct that no safe inference can be made from figures alone. This 
