176 
In Amaltheus the siphonal or abdominal side of the shell 
forms, in general, a more or less sharp keel, often with an 
imbricated edge, and which projects forward in a long pointed 
process. This is very well seen in Amaltheus cordatus (fig. 16), 
where the lateral ribs are observed bending obliquely forwards 
towards the aperture, and the keel projecting onward in a 
long spear-shaped process. In Amal. margaritatus the keel is 
beaded and prominent, the ribs bending forward in graceful 
sweeps towards the aperture. In Amal. owynotus (fig. 17) the 
shell is discoidal, and the siphonal area is almost as sharp as a 
currier’s knife (fig. 18); the sides are undulated, with falciform 
ribs derived from the original form of the aperture, and with a 
projecting ventral process. 
Fie. 17.—Amaltheus oxynotus, Quenst. Fie. 18. 
In Harpoceras, which embraces the true Falcifers (Von Bucn), 
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. 19), in Harp. bifrons, and 
Harp. Levisoni, and long and projecting in Harp. opalinum. I 
