154 PSEUDOCERATITES OF THE CRETACEOUS. 
estimated, is 69.5 mm., the outer portion of this volution, partly estimated, 
is 42.5 mm., the umbilicus is 5 mm. and the opposite part of same volution is 
22 mm. The shell is present on the venter but not on the line of involu- 
tion. Greatest transverse diameter of outer volution is 25 mm., the inner 
‘part is 11 mm., both through the umbilical shoulders, shell on one side and 
not on the other side. Probably shell would have made the difference of 
5-mm. in each case. 
This is a compressed shell, closely similar in aspect to Engonoceras 
uddeni and the ephebic smooth stage of Protengonoceras ? emarginatum, but 
the involution is greater; the costations in this stage are fainter, but can be 
plainly enough seen both on cast and on the shell in a cross light. They 
are less than in Gabb’s figure, but the form of venter and aspect of shell, 
including amount of involution, shows that we are dealing with Gabb’s 
species. There are also no tubercles on the umbilical shoulders. The first 
large fold is partly present on the broken edge of the outer volution in 
the small fragment figured, showing the beginning of the gerontic stage. 
The venter is decidedly concave with slight ridges on either side. This 
form of venter is found in the neanic stage and the whorls, although 
stouter, are similarly compressed when the whole diameter is only 13 mm. 
At diameter of +4 mm. this venter, although almost as broad as the trans- 
verse diameter, is already like that of the adult, but may be a little flatter. 
Other details could not be seen. It is obvious that the young acquire 
the concavity and sharp lateral ridges of the venter in an early neanic 
substage at a time when the volution becomes flattened on the lateral 
zones. The form is then obviously like some stouter and less involute 
forms of this genus not yet discovered. 
The sutures are very slightly flexed apicad; the saddles and lobes 
closely similar to those of Metengonoceras. 
The venter is slightly asymmetrical; the first pair of saddles on the 
right are divided by a very slight marginal lobe. . There are nine saddles 
and eight lobes on the right side, the seventh saddle alone being bifid. 
The marginal lobe dividing this saddle appears on the earliest suture of 
this volution. Lobes on the left side of a more advanced stage show that 
this simplicity is due to age. 
A larger specimen, same locality, in the gerontic stage, is 108.5 mm. in 
diameter and has the shell preserved. Outer part is 57.5 mm., umbilicus 
