1903.] Brown, A New Genus of Ground Sloth. 573 



first molar, marking the boundary of the premaxillary sur- 

 face, is a small deep notch, back of which there is a small 

 expanded area marking the widest part of the maxillaries. 



The palatine is concave and smoother than the maxillary 

 surface; the median sutural line is not prominent. Anteri- 

 orly the palatines join the maxillaries in an irregular suture, 

 anterior to the alveoli of the last molars; laterally it unites 

 with the maxillaries just internal to the alveoli. The pos- 

 terior palatine foramina, situated on the outer side near the 

 origin of the descending pterygoid processes, are the only 

 openings in the palatines. Posteriorly they expand to unite 

 with the orbitosphenoids and are separated by a wide enter- 

 ing notch. 



The pterygoids will be described from the outer aspect. 

 Internally they are convex, with a rugose posterior border 

 forming the lateral boundaries of the large posterior narial 

 opening. 



The sphenoidal bones are not suturally defined from one 

 another: that part forming the roof of the nasal depression 

 between the pterygoids is broadly arched from side to side, 

 and wider than in Adylodon; the surface is smooth with two 

 longitudinal channels parallel to the base of the pterygoids. 

 Posteriorly the narial opening is bounded by two rough sub- 

 elliptical tuberosities. 



The hasioccipital is a broad concave plate, the posterior 

 edge of which is deeply incised, forming the lower boundary 

 of the foramen magnum; the palate is pierced by a small 

 vascular foramen immediately in front of the condyles. The 

 anterior condylar foramina are large, but not more than half 

 the diameter of those in M. rohustus. External to the con- 

 dylar foramen the hasioccipital continues in a strong rough 

 tuberosity forming the posterior inner boundary of the articu- 

 lar depression for the stylohyal, and also the posterior bound- 

 ary of the jugular foramen. The sides of the basisphenoid 

 descend rapidly in front of the jugular foramen, ending in the 

 large tuberosities before mentioned as bounding the posterior 

 narial opening. 



The condyles are rounder and shorter than in Mylodon, 



