EDENTATA OF THE SANTA CRUZ BEDS. 295 



SCHISMOTHERIUM Ameghino. 



(Plates L, LI, LIII, Figs, i, 8.) 



Schismotheriiim Amegh.; Enumeracion sistematica, etc.; 1887, p. 21. 

 Metopotherium Amegh.; Rev. Argent, de Hist. Nat; T. I. 1891, p. 324. 



The diastemata are either absent or extremely short, which imme- 

 diately distinguishes this genus from both Hapalops and Analcimorphus, 

 and in fact, with the exception of Pelecyodon, this is the only genus of the 

 family so characterized. The caniniform teeth vary greatly in size and 

 shape, but they are never large and are usually more or less trihedral in 

 section ; L is somewhat removed from the anterior border of the maxil- 

 lary, though not nearly so far as in Analcimorphus ; - is always styliform 

 and either cylindrical or trihedral ; the molariform teeth are transversely 

 oval and more or less compressed antero-posteriorly, sometimes very 

 strongly. 



The skull is short and broad, with much vaulted cranium and deep 

 postorbital constriction ; the sagittal and occipital crests are better devel- 

 oped than in most of the preceding genera and the former curves forward 

 dorsally in a very characteristic way. The mandible is short, with deep 

 horizontal ramus and broad ascending ramus ; the symphysis is short and 

 steep, the chin very abrupt and the predental beak short and broader than 

 in any of the other genera. 



The fore-limb and foot are of the type common to all the family, but 

 the manus is more isodactyl than in Hapalops. The femur is remarkable 

 for the slenderness and roundness of the shaft, which are even more 

 pronounced than in Analcimorphus. 



While more complete material of this genus is much to be desired, the 

 evidence at hand is sufficient to show that in Schismotherium we have the 

 somewhat modified representative of one of the most primitive members 

 of the Gravigrada and one which is not far removed from the common 

 ancestor of all the Megalonychidce and perhaps of the other two families 

 also, as may be seen from the styliform -, the slender femur and the iso- 

 dactyl feet; it is a very suggestive fact that in the Gravigrada of the 

 Patagonian formation - is almost always styliform, and probably the 

 absence of diastemata is also a primitive feature, but conclusive evidence 

 on this point is lacking. The close relationship of Schismotherium with 

 Analcimorphus is very clear, and through the latter we have the connec- 

 tion with the Planopsidce. 



