EDENTATA OF THE SANTA CRUZ BEDS. 241 



HAPALOPS ATLANTICUS Ameghino 



Xyophorus atlantictis Amegh. ; Rev. Argent, de Hist. Nat.T. I, 1891, p. 320. 

 Xyophorus andinus Amegh.; Ibid., p. 321. 



This species, which is as yet known only from three mandibles in the 

 Ameghino collection, differs from the preceding one principally in size, 

 being much larger and more robust. The lower teeth are similar in char- 

 acter to those of H. rostratus, but the series varies in length from 38 to 

 43 mm.; the horizontal ramus is deeper dorso-ventrally and the preden- 

 tary beak equally short, so that the profile of the chin rises somewhat more 

 steeply forward. The border of the ascending ramus is more inclined 

 backward and the postero-external opening of the dental canal is distinctly 

 lower in position. In the largest of the three individuals the depth of the 

 horizontal ramus below -5 is 30 mm. 



HAPALOPS RECTANGULIDENS Ameghino. 



Parhapalops rectangulidens Amegh.; Rev. Argent, de Hist. Nat., T. I, 



1891, p. 310. 

 Parhapalops rectangiilaris Amegh.; Enum. Synopt. de Mamm. Foss. de 



Patagonie, 1894, p. 146. 

 Eleutherodon heteroclitus Mercerat ; Rev. del Mus. de La Plata, T. II, 



1891, p. 24. 



? Parhapalops pygmcetts Amegh. ; Enum. Synopt. de Mamm. Foss. de 

 Patagonie, 1894, p. 146. 



In almost all of the species of Hapalops the last lower molar is of more 

 or less distinctly cylindrical form ; in the present species, however, this 

 tooth is antero-posteriorly compressed and its principal diameter is trans- 

 verse. In addition to the type in the Ameghino collection, there is in the 

 La Plata Museum a mandible (type of Eleutherodon heteroclitus Mercerat) 

 which agrees well with the type-specimen in size and in the peculiar form 

 of T , though differing very markedly in the shape of ^ and 7 . The analogy 

 of other species would indicate that the agreement in the shape of T is of 

 greater taxonomic significance than the difference of -% and ^. Hence, the 

 two species should be at least provisionally united. 



The first tooth ( T ) has the usual oval cross-section and is separated from 

 ^ by a short diastema. In the type ^ is subquadrate, while in the La 

 Plata specimen this tooth is more antero-posteriorly compressed and trans- 



