224 



THE LIAS AMMONITES. 



Fig. 113. — Amaltlieus oxynatus, Quenst. 



Fig. 114. — Front view. 



In Ilarjjocer^aSjVfVicXx embraces the true Falcifers of von Bacli, the sickle-shaped ribs 

 announce a complicated structure of the mouth-border, with a projecting siphonal or 

 abdominal area, and with lateral lappets of greater or less extent ; they are small in 

 Harpoceras serpentinum (fig. 115), in Harp, bifrons, Harp. Levisoni, and long and 

 projecting in Harp, opalinum. I must refer to the plates of tliese species, and the 

 descriptive text thereof, for many important details concerning the mouth-borders of 

 Harpoceras. 



Fig. 115. — Harpoceras serpenti- 

 num, Schloth. 



Fig. 116. — Stephanoceras 

 Deslonffchampsii, Defrance. 



Fig. 117. Fig. 118. 



Stephanoceras Braikenridgii, showing labial prolongations. 



In Stephanoceras the shell varies in form ; the siphonal or abdominal area is, in 

 general, rounded and without a keel or furrow, and the lateral ribs terminate in tubercles 

 on the sides, from whence numerous folds branch out and extend over the abdomen to 

 join their fellows from the opposite side. The mouth-border in Stephanoceras Desloncj- 

 chaDpsii consists of a thick band which encircles the aperture, as in fig. 116, and, by its 

 prominence and inflexion on the sides, forms the main lateral portion of the ribs up to 

 the tubercles which are prominent in this species. In Stephan, Humphriesianum the oral 



