68 PSEUDOCERATITES OF THE CRETACEOUS. 
but the distance from the last ventral siphonal saddle to the broken edge 
is 22 mm.“ The almost obsolescent traces of sutures of the basal septum 
are only about 5 to 7 mm. from the edge of the aperture on the sides, and 
may have been about 26-30 mm. from the end of the completed rostrum 
on the venter. 
The only explanation that I am able to suggest is that the animal lost 
the power to build shell after it had constructed this aperture, but still 
continued to live and build the sutures until finally the pressure of the 
base upon the last sutures put a stop to their construction near the lines 
of involution, but allowed it to go on with decreasing completeness exter- 
nally. This obliges one to suppose that a futile attempt was made to 
construct the outer three saddles and lobes of the basal septum, and that 
the animal slipped back upon the second septum after failing to do this. 
There are no lines connecting the broken sutures with each other that I 
could detect. The reflected rim of the cast of the aperture near the 
umbilicus in some measure supports the opinion that the animal, failing 
in having a proper shell wall to the living chamber, spread out laterally 
and the reflected extensions of the aperture were built by the lateral parts 
of the body wall that bulged out on either side. In that case the animal 
might have had an abnormally thin-shelled living chamber which was 
destroyed after its death. The questions that such suggestions create are 
far more difficult than I can answer with merely a single cast in hand, and 
an entirely satisfactory solution must be relegated to future investigations. 
A large cast (PI. VII, figs. 1, 2; PI. UX, fig.13) in Coll. Nat. Museum, No. 
2403, from Pontotoc County, Miss., is somewhat over 265 mm. in diameter. 
The diameter of outer volution from line of involution to venter at the 
beginning of last quarter where venter was complete is 136 mm.; same 
diameter opposite this one-half of a volution distant is 92 mm.; smallest 
diameter 79 mm., one-quarter of a volution younger than the last. 
The transverse diameter through the center of sides corresponding to 
first diameter is 57 mm. and for second 39 mm.; the third could not be 
measured. The right side is a little worn away, so that these transverse 
diameters are less than they should be. 
«These sutures are not like the imperfect septa occurring in Bathmoceras and some Orthoceratites, 
since in those cases the animal still continued to have a distinct living chamber. They are in some 
measure similar to those occurring rarely in very old shells. 
