EDENTATA OF THE SANTA CRUZ BEDS. 89 



characteristic. In the movable bands (Plate XVI, fig. 8) the plates are of 

 very different sizes, but are always remarkably broad in proportion to their 

 length, and some of them are almost square; they are quite thin and, 

 when viewed from the side, have usually a more or less distinct sigmoid 

 curvature ; the part of each plate which was overlapped by the preceding 

 one is remarkably short, shorter than in any other known genus, except 

 some of the anterior plates of Stegot her turn ; in the exposed part of the 

 scute are two or three very large and conspicuous pits which were doubt- 

 less for the insertion of tufts of hair, or bristles ; on some of the plates 

 three longitudinal ridges are feebly marked, others show no trace of them ; 

 the surface of the scutes is everywhere coarsely pitted and on the margins 

 are large and probably piliferous pits. The fixed scutes are smaller 

 and thinner than the movable ones, but, except that no part is covered, 

 they resemble the latter in markings and in the presence of the large pits ; 

 these plates appear not to have united with one another suturally, but 

 merely to have been in juxtaposition. According to Ameghino ('94^, 175) 

 a tail-sheath was present. 



Dentition. - - The teeth are hardly less peculiar than the head-shield. 

 The dental formula is y and in both jaws the teeth form a continuous 

 series in a well-defined arch. No diastema is present, but each tooth is 

 isolated by very short spaces, and all the teeth have an external layer of 

 hard and polished dentine, suggesting enamel in appearance. None of 

 the specimens that I have examined shows the suture between maxillary 

 and premaxillary very distinctly, but it would seem that only one tooth 

 was implanted in the latter. When the jaws are closed, the anterior upper 

 teeth pass outside of the lower ones and conceal them from view. The 

 first upper tooth, -, presents directly forward and has a strongly convex 

 anterior face and almost plane posterior face ; the crown is somewhat 

 chisel-shaped, but narrows distally, ending in a blunt point: J - is con- 

 siderably larger and is usually the highest and most prominent tooth in the 

 series, it is of triangular section, with the rounded apex turned forward and 

 with a shallow, vertical groove on the outer face near the posterior border ; 

 the hinder surface is obliquely worn, making the tooth quite sharply 

 pointed : - is generally lower than -, but of somewhat greater diameter and 

 more deeply grooved on the outer face ; it is almost as sharp-pointed : 

 - is similar, but smaller and blunter : - is still smaller and the end is 

 bevelled by wear : A is much smaller and has a nearly horizontal grinding 

 surface : - is extremely small and cylindrical. 



