352 PATAGONIAN EXPEDITIONS I PALEONTOLOGY. 



Gravigrada were now living, we might well include them all in a single 

 family. In the structure of the skull, the vertebral column, the limbs and 

 feet, there is a remarkable uniformity of plan throughout all the genera, 

 and this uniformity is clearly to be interpreted as indicating the common 

 origin of the three families and the relatively small degree of divergence 

 which they had attained in the Santa Cruz epoch, as compared with the 

 differences which separated their Pleistocene representatives. 



NEMATHERIUM ANGULATUM Ameghino. 



(Plates LXIl, Fig. 3 ; LXIII, Figs. 3-50.) 



Nematherium angulatum Amegh. ; Enumeracion sistematica, etc., 1887, 



p. 22. 



Nematherium sinuatum Amegh. ; Ibid. 

 Nematherium longirostris Amegh. ; Rev. Argent, de Hist. Nat., T. I, 



1891, p. 324. 

 Nematherium lavagnanum Mercerat; Rev. del Mus. de La Plata, T. II, 



1891, p. 26. 



This, the typical and most abundant species, is of medium size and is 

 characterized by a certain degree of constancy in the forms of the teeth, 

 though there is much variability also. In the upper jaw - is subcylin- 

 drical, i-A are distinctly triangular and bevelled by wear, with a smaller 

 anterior and larger posterior worn surface ; - is horizontally worn and 

 less distinctly triangular than - or *-. In the mandible T is triangular, 

 -% and ? are quadrangular and lozenge-shaped and is more elongate 

 antero-posteriorly ; T is bilobate, but no two specimens agree in the rela- 

 tive size of the two lobes, which is often different on the two sides of the 

 same mandible. The anterior divergence of the two rows of teeth is 

 more decided than in some of the other species. Of the skull only one 

 imperfect specimen is known and that displays little that is characteristic. 

 The mandible has a long, obtusely pointed predental beak, the dorsal 

 border of which is raised above the level of the teeth ; the ascending 

 ramus is broad and the coronoid erect. 



In the following table the measurements are from the type of N. longi- 

 rostris in the Ameghino collection. 



