PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
I 18 
NESODON Owen. 
(Plates XII-XXVI.) 
Nesodon Owen; Rep’t Brit. Ass. Adv. Science, 1846, p. 67. 
Toxodon Moreno (non Owen) ; Patagonia, resto de un continente hoy 
submerjido, Buenos Aires, 1882. 
Colpodon Burmeister (in part) ; Anales del Mus. Nac. de Buenos Aires, 
T. Ill, Entr., XIV, 1885, p. 161. 
A strapotherium Burmeister (in part) ; Descr. Phys. Repub. Argent., T. 
Ill, 1879, p. 517. 
Protoxodon Ameghino ; Observ. gener. sobre el orden de mamiferos esting. 
sud-amer. llamados Toxodontes, p. 62. La Plata, 1887. 
Atryptherium Ameghino; Enumeracion sistematica, etc., 1887, p. 18. 
Scopotherium Ameghino ; Ibid. 
Adelphotherium Ameghino; Ibid., p. 16. 
Gronotherium Ameghino ; Ibid., p. 17. 
Acrotherium Ameghino (in part) ; Ibid. 
Nesothevium Mercerat; Rev. del Museo de La Plata, T. I, 1891, p. 386. 
Among the Santa Cruz ungulates by far the commonest is the genus 
Nesodon , the remains of which occur in remarkable abundance. Almost 
all parts of the skeleton are fully represented in the collections, sacral and 
caudal vertebrae alone excepted, and even the successive stages of develop- 
ment, from earliest youth to extreme age, may be readily followed. As 
Ameghino has well shown (’91, 357; ’94^, 230), the animal undergoes 
remarkable changes of appearance during the course of development, and 
to these changes are largely attributable the many names which have been 
applied to it. Though not the largest of Santa Cruz mammals, none of 
which are gigantic, the species of Nesodon are among the larger and 
heavier forms and there is no great range of variation in size. 
Dentition (Pis. XIII, XVI-XIX). — Attention has repeatedly been called, 
especially by Ameghino and Lydekker, to the extraordinary changes in 
the character and appearance of the dentition, which in this genus take 
place in the course of individual development. Without a continuous 
series of skulls, representing all the steps of the transformation, one would 
hardly venture to suggest that the earlier and later stages were of the 
same animal. Normally, the number of teeth is still unreduced and the 
formula is that common to all the early groups of placentals, viz., If, Cf, 
