222 PSEUDOCERATITES OF THE CRETACEOUS. 
This saddle may have a simple median marginal saddle or be trifid with 
three saddles, equal or unequal in size; or it may be bifid, with both mar- 
ginals again subdivided, or of any shape between these and such irregular 
sinuous outlines that it is difficult to describe it. It is almost invariably 
sunken between two marginal saddles, one on either side, but occasionally 
even these blend with the central part of the siphonal saddle. 
A specimen from Cheyenne River, South Dakota, in the collection of 
Columbia University, New York City, reaches 327 mm. in diameter and has 
the basal part of a living chamber present. The venter begins to be rounded 
on this living chambered part. There is a slight decrease in the amount of 
involution at the same time, showing that this is in its gerontic stage. In11 
other specimens, in collection of the Boston Society of Natural History, and 
sent me by Ward, ranging in size from 110 mm. in diameter to nearly the 
dimensions of the specimen last described, the typical form was observed. 
No tubercles were present, and the first lateral saddles were very narrow 
and very deeply cut by almost straight and very long marginal lobes and 
saddles. 
In all of these there are chevron marks more or less shown, and the 
sutures are similar, with the exception first mentioned. The first three lateral 
lobes are not very steeply inclined apicad, and the fourth lateral is nearly 
or quite two-thirds as long as the third lateral. 
Altogether I have seen perhaps 40 specimens. 
A specimen from South Dakota, in collection of the Boston Society of 
Natural History, which is 113 mm. in diameter, shows the costz and the 
chevrons, but the costz are quite fold-like. There were no tubercles on 
the edges of the ventral zone nor on the umbilical shoulders. The smallest 
part of the outer volution was about 30 mm. and the widest part about 60 
mm. from line of involution to venter. 
Some of the fragments of volutions examined must have belonged to 
shells fully 15 inches in diameter, the size of the specimen from New Jersey 
figured by Morton as P. placenta, but none of these showed the gerontic 
degenerations in the rounding of the venter as in his figure. The wider 
separation and the simpler outlines of the sutures found in his figure also 
occur only at a comparatively early stage in this species. The ephebic 
stage has narrow concave venter on the thick shell and flattened zone on 
same area in the cast. The sides are perfectly smooth, with faint sigmoidal, 
almost obsolescent, costae. 
