120 PSEUDOCERATITES OF THE CRETACEOUS. 
ends of the lateral costae and there fuse into more or less dichotomous 
forms. This fusion is not as complete in the fossil shown in fig. 16 as it is 
in the one shown in Pl. XIII, fig. 2, at a later age. 
The sutures seem to follow about the same steps in progress of devel- 
opment as the external characters. Fig. 11 gives an enlarged sketch of 
ezecum, which seems small in this specimen and which opens into a large 
siphunele, whose parts could not be studied any further than is visible in 
the drawmg. Although every effort was made, and this specimen was 
remarkably clear and transparent, nothing definite could be made out 
beyond the cecum. It is certain that the dark color of the wall of this 
body has no posterior prolongation or prosiphonal continuation. The 
second septum, beginning the sutures of the metanepionic substage, had 
unquestionably a divided ventral lobe, as given in fig. 10. This was estab- 
lished by many repeated observations. There were, as usual, but two 
broad goniatitic saddles of the Tornoceran type on either side and one 
broad lateral lobe on each side, with a distinct saddle at the line of involu- 
tion. Iwas not able to detect any depression, such as I have previously 
described in other forms as an embryonal umbilicus, occurring at the begin- 
ning of the true conch. In the paranepionic substage the suture becomes 
distinctly divided on the sides into two broad saddles, with a lateral lobe 
and a lobe at the line of involution on either side, and during this substage 
the dorsal suture assumes finally the aspect given in fig. 21. The sutures 
(figs. 18-20, 22) belong to the neanic stage, represented in figs. 12-15. 
They show the usual mode of division common in Ammonoids of the Jura 
and Cretaceous, the incoming of auxiliary inflections ‘on the primitive 
second lateral saddle and the primary bifid division of the first lateral 
~ saddle and first lateral lobe, the entire aspect of the siphonal saddle and its 
subsequent bifidity. Fig. 22 of Pl. XI shows the peculiar prolecanitean 
aspect of the dorsal inflections before the end of the neanic¢ stage, and illus- 
trates my previous statements with regard to the retention of ancestral 
characters by these internal sutures. Fig. 23 of Pl. XI and fig. 1 of Pl. XIII 
are of very nearly the same age, and give the beginning of the ephebic 
substages. The latter show that the primitive median marginal lobe of the 
primitive dorsal saddle becomes the large marginal dividing the full-grown 
first lateral saddles. This suture also shows that the second lateral saddle 
has a trifid termination in some specimens of this species. 
