202 PSEUDOCERATITES OF THE CRETACEOUS. 
inner arm extends inwardly and, being itself bifurcated, gives a trifurcated 
aspect to each of these saddles. The inner lobes are bifurcated and 
broaden outwardly, being somewhat blunt or rounded except in the third 
lateral, which is pointed and apparently of the bifurcated type, as are also 
the other lobes. The last four sutures are more or less approximated, and 
the last two and part of the third interfere, as in P. placenta, except near and 
on the venter. 
The living chamber is one-half of a volution in length. The outer 
part of the aperture is preserved, showing a blunt, broad, rounded ventral 
crest, or slight rostrum, ventro-lateral sinuses on the second line of 
tubercles, and the appearances indicate broad lateral crests, but the margins 
were broken away inside of this. The approximation to P. sancarlosense is 
so close that probably most paleontologists will prefer to consider them 
identical, but the lateral nodes are larger and more quickly developed and 
the ventral tubercles more elongated and more widely separated. The 
extremely thick shell is shown as well as the fact that the ventral tubercles 
are not more prominent on the thick shell than they are on the cast. 
Locality: Fort Worth, Tex.“ 
Age: Probably same as guadalupe and sancarlosense. 
PLACENTICERAS PLANUM n. sp. Hyatt. 
Pl. XX XIII, figs. 2-4; Pl. XXXIV. 
This is also a part of the collection made by Stanton and Vaughan. 
This species also grades into P. sancarlosense although very distinct from 
guadalupe. he sides are almost smooth, the tubercles being very small 
and obscure, except in the umbilicus. The affinities for guadalupe and its 
allies are demonstrated by Mr. Stanton’s care in collecting this fine series. 
The flat, compressed aspect of the young is maintained until the shells reach 
a diameter of 221 mm., and the venter does not show any broadening out 
until after the shell reaches the gerontic stage. 
One of the specimens from Presidio del Norte, No. 21651, is 240 mm. in 
diameter. Four-fifths of the outer volution is in the gerontic stage, but the 
first part of the parephebic substage shows the venter still narrow, flat, and 
tuberculated. It then becomes rounded, but the volution still remains com- 
«Mr. Stanton has commented as follows upon this alleged locality: ‘‘P. sancarlosense var. 
pseudosyrtale, labeled ‘Fort Worth, Texas,’ must have come from some other place, though possibly 
in that region.’’ (See note on P. guadalupz. ) 
