EDENTATA OF THE SANTA CRUZ BEDS. 287 



just external to its junction with the basisphenoid, is a broad, conspicuous 

 groove, leading obliquely into the narial canal. 



The mandible, known only in the type, can be but partially described, 

 because at the time of my visit to La Plata, the jaw was still partly in the 

 matrix, and the ascending rami and the predental beak are broken. The 

 symphysis is very long, extending back nearly as far as ^, and the 

 beak was evidently long, perhaps very elongate, and is but moder- 

 ately concave on the dorsal side ; the ventral border of the horizontal 

 ramus is strongly convex, greatly increasing the depth of the jaw, which 

 below ^ is 47 mm.; the shape resembles the jaw of Megatherium and 

 is quite unlike that of A. inversus, in which the ventral border is almost 

 straight. 



The stylo-hyal (Plate XLVII, Fig. i) agrees in its general form with 

 that of the modern sloths and of the Pleistocene Gravigrada ; it is hammer- 

 shaped, with proximal end expanded antero-posteriorly and compressed 

 laterally ; the surface for the periotic is anterior and forms a small 

 tubercle ; the slender shaft is subcylindrical, with a sigmoid curvature. 



MEASUREMENTS. 



No. 15,561. No. 15,163. 



Skull, length in median basal line 144 .141 



" " condyles to anterior nares ?. 168 .171 



Cranium, length condyle to edge of orbit 132 .130 



Face, length orbit to anterior nares ?-O37 .043 



Occiput, height .042 



" width at base 059 .060 



Skull, width at postorbital constriction 041 .046 



Rostrum, width .037 .041 



Zygomatic arch, length 100 .096 



Palate, length in median line 072 .059 



" width at 1 02 1 .024 



" " "2- 017 .018 



" " " & 016 .014 



Vertebral Column (Plate XLIX, figs, i, 2, 3*). --The atlas is longer 

 than in Hapalops longiceps, with wider neural arch and even more 

 reduced neural spine ; the anterior cotyles are farther apart ventrally ; the 

 transverse process is more horizontal, less extended antero-posteriorly, 

 not reaching to the anterior cotyle, which projects in front of it, and is 

 separated from the posterior cotyle by a deep notch ; on the ventral side 



