222 
PATAGONIAN EXPEDITIONS : PALEONTOLOGY. 
Certain mandibles of Nesodon imbvicatus appear to show a similar 
arrangement of the incisors as an individual peculiarity, but the imperfec- 
tion of the specimens precludes any positive statement regarding them. 
Ameghino regards Adinotherium as the ancestor of the Haplodonther- 
iidae, the family to which he assigns Trigodon. “ Aussi bien les Haplodon- 
theriidae que les Toxodontidae, ils prennent leur origine dans les Nesodon- 
tidae. Les Haplodontheriidae descendent du genre Adinotherium , tandis 
que les Toxodontidae doivent descendre d’une esp£ce du genre Nesodon ” 
(’07, 91). Not at all improbably, this may prove to be the correct inter- 
pretation of the relationships of Adinotherium , but, on the other hand, the 
discovery of a species of Nesodon , N cornutus , which appears to have the 
same small dermal horn as Adinotherium , leads to the conjecture that 
Nesodon may perhaps have been the ancestor of Trigodon. This conjec- 
ture is somewhat strengthened by the fact that in the latter genus the shape 
of the muzzle and symphysial region of the mandible is more as in 
Nesodon , Adinotherium agreeing better in this regard with Toxodon. In 
short, it is possible that Ameghino’s suggestion should be reversed, but 
only the identification of the successive steps of change which led up to 
Toxodon , on the one hand, and Trigodon , on the other, will enable us 
to decide this question. 
Adinotherium ovinum (Owen). 
(Plates XII, Fig. 1 ; XVII, Figs. 4, 5, 7-10; XVIII, Figs. 2, 3, 5; XX, Figs. 1-4; XXI, Figs. 3-10; 
XXVI, Figs. 1-3, 7-12; XXVII.) 
Nesodon ovinus Owen ; Phil. Trans., 1853, p. 291. 
? Adinotherium inagister Amegh.; Enum. sistem., etc., 1887, p. 17. 
Adinotherium proximum Amegh.; Ibid. 
Adinotherium ferum Amegh.; Ibid., p. 18. 
? Acrotherium mutabile Mercerat ; Rev. del Mus. de La Plata, T. I, 1891, 
P- 393- 
? Nesodon typicus Mercerat; Ibid., p. 402. 
? Adinotherium haplodontoides Amegh.; Rev. Argent, de Hist. Nat., T. I, 
1891, p. 129. 
Adinotherium ovinum (Owen) Amegh.; Ib’d., p. 376. 
Adinotherium Kobyi Mercerat; Rev. del Mus. de La Plata, T. I, 1891, 
p. 410. 
