EXTINCT CATS. 283 
lower jaws, and the generic determination cannot be regarded 
as altogether free from doubt until the upper carnassial tooth 
be discovered. 
III. GENUS MACHARODUS 
Machairodus, Kaup, Oss. Foss. Darmstadt, pt. 2, p. 24 (1833). 
Agnotherium, Kaup, op. cit. p. 28. 
Steneodon, Croizet, Rev. Encyclop. vol. lix. p. 76 (1833). 
Cultridens, Croizet, in Huot’s Nouv. Cours. Elém. Géol. vol. i. 
p. 265 (1837). 
Smilodon, Lund, K. Danske, Vid. Selsk. Skr. vol. ix. p. 293 (1842). 
Meganthereon, Pomel, Cat. Méthod. p. 58 (1853). 
Drepanodon, Bronn, Lethza Geognost, vol. ili. p. 1115 (1853- 
56). 
Trucifelis, Leidy, Proc. Acad. Philad. 1862, p. 175. 
The Sabre-toothed Tigers, as the members of this genus are 
commonly called, are easily distinguished from the True Cats 
by the enormous development of the upper canine teeth, which 
frequently have serrated cutting edges, and were protected by 
a downward flange-like expansion of the front of the lower jaw, 
against which they rested when the mouth was closed. These 
animals were common to both the Old and New Worlds, and 
some of the Pleistocene species attained very large dimensions; 
the exposed portion of the highly compressed canines of a 
South American species measuring upwards of seven inches 
in length. That these Cats were the most specialised of the 
entire Family, may be considered certain ; but there is great 
difficulty in understanding how they made use of their tusks, 
since when the mouth was open these would extend right 
across the opening, and it is almost impossible to believe that 
they could have been used with the jaws closed. The oldest 
representative of the genus is AZ. zusignis from the Upper 
Eocene (Oligocene) Phosphorites of Central France. In the 
Middle Miocene of France and Styria we have AZ, palmidens 
and JZ. jourdani ; and in the Lower Pliocene of Darmstadt, 
