THE LIAS AMMONITES. 
Fig. 113. — Amaltheus oxynatus, Quenst. Fig. 114. — Front view. 
In Harpoceras, wliicli 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 
Harpocerus serpentinum (fig. 115), in Rarp. bifrons, Harp. Levisoni, and long and 
projecting in Harp, opalinmn. I must refer to the plates of these species, and the 
descriptive text thereof, for many important details concerning the mouth-borders of 
Harpoceras. 
Fig. 115. — Harpoceras serpenti- Fig. 116. — Stephanoceras Fig. 117. Fig. 118. 
num., Schloth. Deslongchampsii, Defrance. Stephanoceras BraiJcenridgii, 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 DesJong- 
champsii 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. Himphriesianum the oral 
