124 PSEUDOCERATITES OF THE CRETACEOUS. 
tubercles and the second lateral row disappear on these coste. The 
decrease of the involution through shrinkage of the later diameters is 
greater in this than in the old age of the specimen shown on PI. XIII, 
fig. 4. Breadth of the side from line of involution to the siphonal saddle 
at the suture figured is 65 mm. The length of the living chamber on the 
outside or venter is 190 mm. and apparently complete, and the breadth 75 
mm. In the specimen shown in Pl. XIV, fig. 7, the normal rate of increase 
is from 50 to 70 mm. in the same distance measured along the venter, and 
in the living chamber of the fossil shown on Pl. XIII, fig. 4, which is of the 
same length on the venter it is from 7) at the base to 80 mm. near the end: 
In both of these old specimens the length of the living chamber and 
decrease in the rate of growth was therefore about the same and about 
one-half of what it was in the fossil shown on Pl XIV, fig. 7, which was 
also an old specimen but was measured along the septate and therefore 
younger portion of the outer volution. The increase by growth previous 
to this must have been greater still, The broadening of the venter 
noticeable near the aperture (figs. 3 and 4), the spreading of the cost 
across the venter, and the loss of nodes are the same in all three of these 
specimens and show them to have entered upon the last or paragerontic 
substage or decline. The youngest suture examined in this species is 
shown in Pl. XIV, fig. 8, from the left side, and this has fully entered the 
ephebie stage and is already more complex than those of swallovt at a much 
later age. The corresponding suture on right side of the same specimen is 
similar, but the third lateral saddle was quadrifid instead of bifid and 
the fourth lateral was more distinctly bifid and phylliform. The matrix of 
this fossil from Elm Fork, Tex., was a gray limestone, whereas that of the 
specimen shown (fig. 9) was a red clayey limestone, but from the same 
locality. The suture was much older, but nevertheless had simpler third 
and fourth saddles on both sides of the outer volution. The position of 
the suture of the specimen shown in fig. 7, given in fig. 8, is indicated in 
fig. 7 by a straight line near the venter, but the sutures throughout this 
volution have the same outlines. This and fig. 10 are the most complex 
of the full-grown sutures observed in this: species. 
Fig. 10 was taken from the left side of Pl. XIII, fig. 4, and shows 
the outlines of about the same age as in PI. XIII, fig. 8. The shell was 
stripped from a part of the fossil shown in PI. XIII, fig. 4, also, and the 
corresponding suture on that side also observed. In this way it was found 
