226 PSEUDOCERATITES OF THE CRETACEOUS. 
tuberculated and stouter forms P. bolli. The same characters also show 
that these species are not identical, since they are not so strongly developed 
at any stage as in other species, and are succeeded by distinct sutures in 
the nearly full-grown shells. This study suggests also that the western 
species was derived from the eastern form. 
A specimen purchased from Professor Ward, locality Bad Lands, near 
Black Hills, South Dakota, shows the typical sutures and form of whitfieldi. 
The first lateral saddles in the ephebic stage have the usual three nearly 
equal marginal saddles and lobes, and there are no tubercles nor any coste 
appreciable to the eye at diameter from lines of involution to venter of 
101 mm. These sutures, however, have one peculiarity, probably of essen- 
tial service to this investigation. In so far as the first two saddles and 
lobes are concerned, they are appreciably distinct, the first saddles beg 
entirely free. The remaining parts of the sutures overlap more or less, 
as in almost all of this species. In the anephebic substage, or last of 
neanic stage, however, the diameter of volution being 33.5 mm., the costee 
are apparent and have the usual form, but are very faint. The chevrons 
are especially well shown in the fossil, although not more prominent than 
in many other specimens. They were plainly seen on this fragment, 
broken out of the larger volution, and there appeared to be some connection 
between these at their line of convergence and the indistinct longitudinal 
ridge or trace, which is obviously the centran lateral ridge seen in some 
older shells. The sutures are similar to those of the adult at the diameter 
of 24 mm. from lines of involution to venter, but they are easily separable 
by the eye. 
The earlier probably paraneanic substage dissected out from this was 
perfect and measured 26.5 mm. in diameter of the coil. The larger end 
of the volution in this was 15 mm. from line of involution to venter, and 
when the volution was about 11 mm. in same diameter the chevrons and 
costes and excessively faint longitudinal ridges began to appear. There 
were as many as three of these along the centran lateral aspect of the 
volution and shorter but discontinuous ones arising from the chevrons. 
These could only be seen by careful and prolonged observation of the 
nacreous layer, which was preserved on one side. The sutures were less 
crowded than in the young one above described and favorable for obser- 
vations at diameter just noted. There were ten lobes in all, including one 
