174 
of the classification of the Ammonrtip#, and have shown that 
the points of the foliations are all directed backwards towards 
the winding of the spire, and the concavities all look forward 
towards the aperture (as 
seen in figs. 5, 6) in 
the ramified foliations of | 
the suture-line; when they 
are folded the elevations 
are called saddles, and the 
intervening depressions 
lobes. In the Ceratites’ 
these parts are very simple, 
as shown in Ceratites nodo- 
sus (fig. 10), where the 
ere relies wom, Dota dentated saddles are seen 
to point backwards and the 
rounded lobes look forwards. Those parts are more complicated 
in Amaltheus margaritatus (fig. 4), and still more so in Phyl- 
loceras heterophyllum (fig. 6), in which the auxiliary lobes are 
numerous and well developed. Figs. 5, 6 show the disposition: 
of the lobes of this beautiful Ammonite from the Upper Lias. 
Secondly.—The shape of the aperture and the structure and 
development of the mouth-border of the shell vary very much 
in the different groups, and the special form which the border 
presents in different Ammonites affords an element of import- 
ance in constructing the diagnosis of genera. The difficulty 
which the Paleontologist experiences in obtaining Ammonite 
shells, or moulds of such, in which the mouth aperture with 
its border is preserved, has long prevented this anatomical 
character from being used in constructing the diagnosis of the 
different groups; at length, however, many specimens have been . 
found, and we have ascertained that important differences do 
exist, and, perhaps, many more will be discovered by continued 
researches made along the same line of investigation. 
In Arietites, as seen in Arietites. rotiformis (fig. 12), and 
Arietites obtusus (fig. 13), the sides of the mouth-border are 
simple, and the ventral portion is more or less produced, as 
