180 
which I obtained from the Upper Lias at Whitby, of this I 
have given a figure in my Plate two-thirds natural size. 
A remarkable form of mouth-border has been figured by 
Count Minster, under the name Scaphites refractus (fig. 29). 
‘In this species the abdominal or siphonal area forms a beak- 
shaped process, curved downwards towards the aperture, and 
the lateral processes rise into angular projections, producing a 
curious pentagonal-shaped oral aperture in this shell. 
Fre. 29. Fie. 30. Fig. 31, 
Scaphites refractus, Miinst. Ammonites Aon. Miinst. 
A still more remarkable mouth-border is seen in the curious 
Ammonite figured by Von Haver as Am. delphinocephalus, 
in which the siphonal area becomes inflated, and projects 
forward like a Scaphite in a remarkable peak-shaped promi- 
nence. Minster has figured a remarkable fossil, Amm. Aon. 
(figs. 30, 31,) in which the ornamentation of the shell indicates 
a singular structure of the mouth-border. 
Thirdly.—lf the structure of the mouth-border shows that 
Ammonites varied much in the anatomy of their head, mantle, 
and arms, the length of the body-chamber affords another 
character from which important deductions may be made, as 
the capacity of this chamber was doubtless proportioned to the 
size of the contained animal, as seen in the Nautilus pompilius 
(fig. 32) of our seas, where the Mollusc is represented occupying 
the entire body-chamber, the outer margin corresponding to 
the ventral surface, and the columellar side to the dorsal surface 
