1 82 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 
Protoxodon americanus Merc.; Ibid., p. 431. 
Protoxodon decrepitus (Amegh.) Merc.; Ibid., p. 432. 
Protoxodon Henseli Merc.; Ibid., p. 435. 
Protoxodon speciosus Merc.; Ibid., p. 436. 
Adelphotherium lutarium Merc.; Ibid., p. 438. 
Adelphotherium trivium Merc.; Ibid., p. 438. 
Adelphotherium repandum Merc.; Ibid., p. 439. 
Adelphotherium Rothi Merc.; Ibid., p. 440. 
Adelphotherium pumilum Merc.; Ibid., p. 440. 
Nesodon marmoratus Amegh.; Rev. Argent, de Hist. Nat., T. I, 1891, 
P- 377- 
Nesodon ob literatus Amegh.; Ibid., p. 377. 
Nesodon cavifrons Amegh.; Enum. synopt., etc., 1894, p. 23. 
Nesodon brachycephalus Amegh.; Ibid., p. 24. 
“In the whole course of zoological literature there is, I think, nothing 
to compare with the appalling synonymy of this and the following species 
[N ovinus\ ” (Lydekker, ’93, 26). While this is true, the reason for the 
great multiplication of names is not far to seek ; it lies in the extraordinary 
changes in the character of the dentition during the course of individual 
development, which alter the whole appearance of the animal. This was 
first pointed out by Ameghino (’9 1 7/ ) , who showed that the initial con- 
fusion arose from the fact that the type of the species, which is an imma- 
ture animal with the milk-dentition, was described by Owen as an adult. 
In the long list of synonyms given above, it may well eventually prove 
that several of the names refer to species distinct from N imbricatus ; 
all that their inclusion in the list implies is, that their claim to separation 
has not been proved. In his revised lists of the species of Nesodon Ame- 
ghino (’94", 23-24; ’94 3 , 244-5; ’98, 156) retains five, of which only two 
can be regarded as well established. Of the others, one or more may be 
distinct, but the available specimens are insufficient to demonstrate this. 
Both in this genus and in Adinotherium Ameghino employs the character 
of the fronto-nasal suture as a means of specific distinction, referring to N 
imbricatus most of those skulls in which the posterior ends of the nasals 
are separated by large triangular processes of the frontals and to N. mar- 
moratus those in which the nasal processes of the frontals are absent, the 
nasals are in contact with each other throughout their length and are 
received into a deep emargination of the frontals, as in Adinotherium. 
