226 



THE LIAS AMMONITES. 



mantle around the mouth-border of the species possessing these fimbriated projections. 

 A similar structure is likewise found in Lyt. hircinum, from the Lytoceras Jurense zone. 



Fig. 123. — Lytoceras^ flmhriaiiim. Sow. 



Fig. 124. — Phylloceras heterophyllum. Sow. 



In Fhylloceras the involute shell of this group is marked with true forward inclined 

 lines of growth, indicating the presence of a ventral process at the abdominal side of the 

 mouth-border, and this appears to have been the case in the only specimen with a fan- 

 shaped body-chamber, Thylloceras heterophyllum (fig. 124), which I obtained from the 

 Upper Lias at Whitby, of which I have given a figure on my Plate two thirds natural size. 



A remarkable form of mouth-border has been figured by Count Miinster under the 

 name Scaphites refractm (fig. 125). 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. 



Fig. 125. Fig. 126. Fig. 127. Fig. 128. 



Scaphites refractus, Miinst. Lobites delphinocephalus, Hauer. Trachyceras Aon, Munst. 



A still more remarkable mouth-border is seen in the curious example figured 

 (fig. 126) Lobites delphinocephalus, Von Hauer, in which the siphonal area becomes 

 inflated and projects forward as in a Scaphite in a remarkable peak-shaped prominence ; 

 Count Miinster, has figured a remarkable fossil, Trachyceras Aon (figs. 127, 128), in 

 which the ornamentation of the shell indicates a singular structure of the mouth-border. 



1 Written Aegoceras in error on page 198. 



