COILOPOCERATID ®. 97 
specimen, and its original length is not clearly indicated by any marks on 
the exposed volution. The shell is only partly preserved, but it is sufficient 
to enable one to state that there are no tubercles nor distinct cost on 
either shell or cast. 
The venter is subacute and appeared at first to be solid, but close 
examination showed a small core of light-colored filling and a fine darker 
layer between this and the large siphuncle. The small size of the core was 
due to the great age of the specimen, and probably at a still older age the 
keel was entirely solid. The last part of exposed volution is obviously in 
the extreme gerontic stage, since the line of involution has retreated consid- 
erably from the previous normal line of involution, beginning its departure 
on the first quarter and thus greatly enlarging the diameter of the umbilical 
opening. The diameter of widest part is 40 mm. without the shell; with 
the shell it was 8 mm. less, whereas that of the opening in next inner 
volution was only 10 mm. with the shell on. The oldest sutures were 
closer together, and, like the decrease of involution, indicated that the 
specimen was outgrown; but these did not show the extreme degeneration 
sometimes found at the end of the paragerontic substage. The sutures on 
last half of the exposed volution were not in good condition and those 
described below were about the middle of the volution, or in what I took to 
be the metagerontic substage.. The sutures were at this time separated by 
a good interval, the first overlapping being between the fourth saddles and 
the inner side of the third lobes. The next overlapping was between the 
seventh saddles and continued thence to umbilicus. The first lateral saddle 
on left side is very broad and of the trifid type, and the marginal saddles 
elongated and phylliform in outline. It has an inner branch which is 
phylliform, and although it might be reckoned as the second lateral, is only 
a marginal, as in other forms of this genus. The corresponding marginal 
in novimexicanum is smaller, and is not at all likely to be mistaken for a 
second lateral saddle. 
The second is somewhat larger and less phylliform than this branch of 
the first lateral, but has similar characters. The third is still longer and 
larger and has lost more of its phylliform aspect through the development 
of the long marginal lobes. he fourth saddle is very long and large, 
rising above the level of the first laterals, and is deeply cut and 
unsymmetrically trifid, each branch being subdivided except the central 
MON XLIV—03——7 
