SCOTT: TOXODONTA OF THE SANTA CRUZ BEDS. 
221 
avant. La surface de cette protuberance est tres rugueuse, la partie se 
trouvant dans cette condition parfaitement delimitee de la partie lisse, de 
sorte qu’il ne peut rester aucun doute que cette bosse servait a supporter 
une forte corne qui etait inclinee en avant” (t. c., p. 57). Another 
remarkable peculiarity of Trigodon is that in the mandible the number of 
Fig. 41. 
Trigodon gaudryi. Skull, left side, about ^ nat. size. From a photograph of a specimen in 
the Ameghino collection. Monte Hermoso beds. 
incisors is uneven, 5 instead of 6, the unpaired one standing in the 
median line of the symphysis. So many individuals have been found, 
all of which show the same curious arrangement, that the chance of its 
being an abnormality is very small ; both Lydekker (’93, 20) and Ame- 
ghino (’07, 55) agree in regarding it as normal and constant in the genus. 
Unusual as the condition is, the fact of its constant occurrence may be 
accepted without difficulty, though few, I think, will be inclined to follow 
Ameghino in believing that the unpaired tooth has been formed by the 
coalescence of the two median incisors. 
