a4 PSEUDOCERATITES OF THE CRETACEOUS. 
ROEMEROCERAS SUBPLANUM un. sp. Hyatt. 
Pl. II, figs. 4-6. 
This specimen is a cast, whole diameter 55 mm _ The lateral zones 
are flatter than in R. syriaciforme and denticulatwm, and the outer nodes are 
smaller, more acute, and have slight ridges or orad continuations in some 
eases. The inner nodes are also smaller in the young and increase very 
rapidly in size on the last volution and then suddenly disappear, the volution 
becoming at the same time contracted to a subquadrate outline. There 
are four small and three large nodes on the inner line, the place where the 
fifth node ought to be is vacant, and there are fifteen nodes on the outer 
line. The living chamber, which is probably very nearly complete, is less 
than one-half of a volution in length The last two large nodes of the 
inner line are on this chamber. 
The sutures have very broad, short, simple saddles and very short 
lobes. They are similar to those of R. denticulatum but have not such 
complex outlines. The last six sutures are nearer together and become 
finally closely approximated, showing that the fossil is probably an out- 
grown shell. This cast having been cracked open, it was possible to study 
exactly the contact of incrusting ostreans with the surface. It was found, 
as in other cases described, that no shell layers were present, the ostrean 
having grown directly upon the surface of a fossil cast. The shell is 
present in the impressed zone where it is protected’ by the enveloping 
volutions, and it is there thick and well defined. 
Locality: Cajamarca, Peru. 
Age: Upper Cretaceous. 
PSEUDOTISSOTIID Hyatt. 
If the position here taken is correct, the genera assembled under this 
name are distinct from those heretofore included under the Tissotiidee 
They include forms from the discoidal channeled and keeled Pseudotissotia 
in the Turonian to the highly involute compressed Plestotissotia of the 
Senonian. The lobes have the same denticulated outlines as in Tissotide, 
but the saddles are more complex, being denticulated in all the genera 
except Plesiotissotia, in which they are all bifid, the first lateral saddles 
being quadrifid according to Peron’s figure. 
