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PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
rium the frontals usually have no nasal processes and, when present, these 
processes are always very small, while in Nesodon they are commonly 
large and conspicuous, but may be entirely absent, and every gradation 
between the two extremes may be found in any large series of skulls. 
In the original description of most of the species (Amegh., ’87*, 17, 18) 
they are distinguished almost entirely by differences of size, but in the 
latest paper (’07) the diagnoses and descriptions are much more full and 
complete and deal largely with the characters of the skull, distinguishing 
the species in what appears, at first sight, to be a very satisfactory man- 
ner. I have, however, found the greatest difficulty in applying these 
definitions to the material contained in the Princeton and New York col- 
lections. Not only does Ameghino take no account of individual and 
possible sexual differences, but the characters upon which he lays the 
chief stress are combined in a very different way in the material before 
me from the association of features found in his specimens. To adopt 
his method would involve a great increase in the number of species, for 
hardly any of the skulls at my disposal agree at all closely with his 
descriptions and figures and there is such variation among them that any 
constant characters are very difficult to find. It is just here that the lack 
of stratigraphic information makes itself so painfully felt and it may very 
well turn out, when that information shall have been secured, that several 
of the species, here regarded as synonyms, are entitled to recognition. 
The arrangement of species which follows is, it must again be empha- 
sized, purely tentative and is founded upon the assumption that the 
females were hornless and that the males, of most of the species at least, 
possessed a small frontal horn, or possibly a pair of such horns. 
The Systematic Position of Adinotherium. 
In the paper already so often cited (’07, 57-59) Ameghino reports the 
extraordinarily interesting and unexpected fact that the genus Trigodon 
(or Eutvigodon, as it was formerly called) from the Monte Hermoso beds, 
possesses a very large and conspicuous, median, frontal boss, which must 
have served in life to support an unpaired dermal horn, like that of cer- 
tain rhinoceroses, especially, though on a far smaller scale, like that of 
Elasmotherium. “Cette protuberance s’eleve graduellement du bout 
anterieur du plan sagittal vers l’avant, mais dans la partie anterieure elle 
descend brusquement, de sorte que la bosse entire semble penchde en 
