62 PSEUDOCERATITES OF THE CRETACEOUS. 
On the third quarter folds take the place of tubercles of outer row, and on 
the fourth quarter the venter becomes gradually rounded. This shifts the 
greatest transverse diameter from the central parts of the sides to nearer 
the venter. There is also a very slight decrease in the amount of involution 
internally. 
The living chamber is only in part preserved. The younger sutures 
are like those of the same age in the smaller specimen, but are a trifle more 
complex in outline and the ventral lobe seemed to be shorter. This last, 
however, could not be made out clearly anywhere. The general character 
of the sutures is the same as in the younger specimen, so far as all of the 
remaining lobes and saddles are concerned, and there are five divided 
saddles. The first and second lateral saddles are probably bifid, in the 
young becoming trifid later and perhaps bifid again in extreme age.“ The 
third is trifid, becoming quadrifid later. The fourth is trifid throughout. 
The remainder are same as in younger specimen. Lobes appear to be 
about the same as in that specimen. The last two sutures are so close 
together that they overlap more or less throughout, and the third suture 
approaches nearer to the second than in younger parts of this volution. 
This specimen had, therefore, in all its characters probably completed its 
cycle of development and was in the paragerontic substage. There are 
constantly five divided saddles on both sides of specimens of this species so 
far as seen by me. ' 
A perfect cast (PI. IT, figs. 7-12), labeled Rio Pecos,’ in collection of 
Columbia University, is 60 mm. in diameter. The outer volution measures 
32 mm., transverse diameter is 13 mm., the umbilicus 3.5 mm., the opposite 
24.5 mm., and the transverse diameter between tubercles of inner row 9 
mm. The outer volution has already begun to show a blunted or rounded 
venter, and the two rows of elongated nodes are more distinct than in other 
specimens described. These also begin to become rounded on the last part 
of the outer volution. This is as much altered in the form of the volution 
G. e., venter is as blunt) at this size as a second specimen from same 
locality (PI. II, fig. 1 (suture), and Pl. V, fig. 3) at diameter of 86 mm 
“The condition of the sutures of the paragerontic stage made this observation somewhat doubtful, 
because when slightly worn away the saddles lose their secondary divisions and become bifid, the 
central marginal lobe being always more persistent on account of its greater penetration into the 
interior than the more recently acquired marginal lobes on either side of it. 
>See Mr. Stanton’s note, p. 65. 
