PLACENTICERATID ®. 209 
There is a thick, opaque, horn-colored outer layer, an intermediate 
crimson-red layer, and an inner nacreous layer of the usual color. These 
consist of a number of minor layers as in other shells of this genus. The 
sutures have broader lobes and narrower saddles than in whitfieldi and 
placenta, and the outlines of these are somewhat less complicated and not 
so overlapping. The ventral lobe has the same narrow character and 
syrtale-like branches, with large siphonal saddle, as in Meek’s figure of 
P. intercalare, but the siphonal saddle is smooth and entire on the venter, 
as in P. whitfieldi, and also has the same minute marginal saddles on either 
side of this entire center. A fine young specimen of this species, from 
Sage Creek, South Dakota, No. 2104b in collection of Yale Museum, at 
diameter of 80 mm., shows the beginning of the large tubercles of umbilical 
shoulder, the ventral tubercles, and apparently those of the middle row to 
be on the first quarter of its outer volution. This shell must have been 
smooth and similar to P. placenta, perhaps, even in the sutures, when the 
diameter from line’ of involution to venter was about 15 mm. At later 
stages the sutures are distinct. Another specimen, same locality and 
collection, at diameter of 132 mm., shows three rows of tubercles distinctly 
visible on both east and shell, No 2104a. The median lateral lines of 
tubercles disappear on the last quarter of the outer volution in this 
specimen, but the ventral inner rows persist. As long as the median rows 
of tubercles exist the shell has a transverse outline distinct from that of 
whitfieldi at any stage, but when these disappear it is difficult to separate 
this specimen from whitfieldi. I have not yet seen a specimen in which the 
ventral rows of tubercles disappear, but whether they do or not it must be 
impracticable in some specimens to separate them from whitfieldi var. 
tuberculatum, although most specimens are distinct on account of the size 
-and persistence of all of the tubercles. 
A fine specimen from same collection from Sage Creek, South Dakota, 
(No. 1863) at diameter 144 mm., has already passed well into its gerontic 
stage, whereas the specimen figured by Meek is not so far advanced in age. 
The first part of the last volution is considerably compressed, as in Meek’s 
figure, but on the living chamber on the last half of this volution the whorl 
becomes stouter. This chamber is apparently nearer complete and about 
one-half of a volution in length. All three lines of tubercles persist and the 
ventral ones which are alternate in the ephebic stage are approximately 
MON XLIV—03——14 
