214 Bulletin of Laboratories of Denison University voi. xi.j 
It 
Placenticeras placenta^ Dekay. 
This delicate species is also from the septaria concretions 
in the Rio Puerco valley. 
Placenticeras costaia, sp. n. 
Plate XXVIII, Figs. 2-3. 
Shell lenticular, compressed, of moderate size ; umbilicus 
very small ; volutions deeply embracing, widest a little distance 
from the umbilicus ; dorsum flat or slightly channeled, crossed 
by a continuation of the nodes ; surface marked by numerous 
irregular subtriangular and curved ribs, the larger ones extend- 
ing from the dorsum to the ujjibilicus and separated by one or 
more short oblique ribs originating on the dorsum where they 
give rise to small elongate nodes ; aperture apparently narrowly 
cordate, flaring on either side of the volution embraced by it ; 
septa moderately distant, siphonal lobe wider than long, with 
lateral divaricating branches ; first lateral lobe small with two 
lateral projections and trifid terminal portion ; first lateral sinus 
much broader than the lobe, composed of four portions, the 
median one five-digitate at the end and with a spur at either 
side, two small branches on the peripheral side and a small trifid 
branch on the umbilical side; second lateral sinus broken by 
two small spurs ; third lateral lobe with five terminal and two 
lateral projections; remainder of sutural pattern unseen. This 
shell resembles i^ many respects Placenticeras placenta, from 
which it differs not only in sutural pattern but also by the pres- 
ence of well-defined ribs. In this respect it resembles the Mex- 
ican form^ reported by Gabb, Pal. Cal., Vol. II, Fig. 258, which 
seems not to be Ammonites piedernalis, von Buch. Diameter 
of only specimen seen 95 mm. maximum thickness 21. mm. In 
septaria concretions of the Rio Puerco valley associated with 
Buchiceras swallovi, Placenticeras placenta, etc. 
Scap kites nodostis^ Meek and Hayden. 
Our material is all of too fragmental a character to admit 
of more than doubtful identification, but indicates a rather 
large species with the nodose surface characteristic of the species 
