376 S. W. WILLISTON 



skeletal bones, are merely ontogenetic or individual. Typically— 

 that is, those adult skulls associated with the largest vertebrae, 

 and doubtless belonging with the largest humeri and femora — 

 there are fourteen teeth in the maxilla, with the shapes as shown 

 in the illustrations (Fig. 3, F, A), that is, with the first four rather 

 slender and of nearly equal length; the next four are a little broader 

 at the base, though but little longer; with the ninth they increase 

 in size, both in length and breadth, reaching the maximum in the 

 twelfth; the thirteenth and fourteenth decrease a httle in length. 

 Possibly there is a smaller one beyond these, but if so, I cannot 

 distinguish it. This is the condition in both maxillae in one speci- 

 men lying in the matrix, in which the teeth have not been injured 

 in preparation. In another skull the number of teeth is the same, 

 but the ninth to the eleventh are not noticeably larger than the 

 preceding ones. In a third specimen, one of the larger ones, I 

 count fourteen teeth in the maxilla, but the last three are small. 

 Finally, in still another specimen, comprising only the maxilla, 

 mandible, face, and anterior palatal bones, fifteen teeth are pre- 

 served in the maxilla, with an alveolus for at least one more, and 

 probably alveoli for two more. These teeth, moreover are all 

 smaller than in the other specimens and are of uniform size through- 

 out. The teeth are all simple, without accessory cusps of any 

 kind. They are somewhat wider at the base than long antero- 

 posteriorly and are beveled on the inner side. They are somewhat 

 flattened on the outer side and are obtusely pointed. They are 

 thecodont or protothecodont. 



This description in the main seems to agree with that given by 

 Broom' of Ophiodeinis, though some effort is required to under- 

 stand his description. One does not feel sure, for instance, what 

 the antecedent of "it" is in the twentieth line of his description 

 of the teeth, but I assume that it refers to Ophiodeirus. In the 

 typical Araeoscelis it is the last or sixteenth tooth of the series which 

 is smaller, while in Ophiodeirus, if I understand the description 

 correctly, the fourteenth, fifteenth, and sixteenth teeth are smaller. 

 He also described the teeth of Ophiodeirus as cuspidate ; they are 

 not at all so in Araeoscelis. 



' Bull. Amer. Mus. Nat. Hist. (1913). 



