SCOTT : LITOPTERNA OF THE SANTA CRUZ BEDS. 



145 



Theosodou Frenzeli Mercerat ; Ibid. 



Theosodon lydekkeri Amegh., in part ; Rev. Argent, de Hist. Nat., T. I, 



1 89 1, p. 294; Enum. Synopt, etc., 1894, p. 28 ; Les Ongules fossiles 



de r Argentine, Rev. del Jard. Zool. de Buenos Aires, T. II, 1894, p. 



280. 

 Oxyodontotherium lydekkeri Lydekker ; Anales del Mus. de La Plata, T. 



II, 1893, p. 66. 

 If the restriction of the name T. lydekkeri to the larger animals, as sug- 

 gested in the foregoing paragraphs, be correct, the oldest name available 

 for the present species is T. lallemanti Mercerat, though our knowledge 

 of the animal is almost exclusively due to the work of Ameghino, who has 

 briefly described and fully illustrated the dentition, skull and feet. 



T. lallemanii, which is much the commonest of the Santa Cruz species, 

 may be distinguished not only by its size, but also by certain features in 

 the dentition and skull. The upper molars may or may not have the two 

 inner cusps connected by a cingulum and thus in worn teeth either two or 

 three enamel lakes may appear, a very variable feature. The milk pre- 

 molars are quite different from those of T. lydekkeri, dp- and - having 

 much smaller and more symmetrical internal crescents and less developed 

 pillars on the external face. The sagittal crest is high and thin, expanding 

 anteriorly into a long, narrow sagittal area. The nasal processes of the 

 frontals are very short and narrow, and the nasals, though greatly shortened, 

 are longer than in T. garrettorum, projecting farther in advance of the 

 maxillary border, and are in contact throughout their length. 



In the table, No. i is the type of T. lallemanti and No. 2 that of T. 

 frenzeli, the dimensions in both cases being taken from Mercerat's paper. 



Measurements. 











No. 



No. 



No. 



No. 





15,216. 



I. 



2. 



16,003 



I^, length 







.0108 





Upper premolar-molar series, length . 













■131 



" premolar series, length 













.071 



pi, length (i. e., antero-posterior diameter) 











.015 



.013 



" width {i. e., transverse diameter) . 













.010 



P^, length 









.0178 



.0169 



.018 



" width 













.018 



P^, length 









.0179 



.018 



.020 



" width 













.021 



pi-, length 









.020 



.0206 



.018 



