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 MACPLERODUS 

 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. Elem. Geol. vol. i. 



p. 265 (1837). 

 Smilodon, Lund, K. Danske, Vid. Selsk. Skr. vol. ix. p. 293(1842). 

 Megantherecm, Pomel, Cat. Method, p. 58 (1853). 

 Drepanodon, Bronn, Lethaea Geognost, vol. iii. p. n 15 (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 M. insignis from the Upper 

 Eocene (Oligocene) Phosphorites of Central France. In the 

 Middle Miocene of France and Styria we have M. palmidens 

 and M. jourdani ; and in the Lower Pliocene of Darmstadt, 



