686 Bulletin American Micseum of Natural History. [Vol. XIX, 



Materials. — The skull lacks only the distal portions of the 

 postfrontal horn cores, the nasals and their horn core, and a 

 portion of the premaxillary bones. The rostral bone was 

 found displaced but a short distance to the rear on the right 

 side of the muzzle, while on the other side lay the left mandi- 

 ble in perfect condition. The coossified right angular and 

 articular, together with portions of both splenials, were found 

 beneath the skull. One badly preserved humerus, half of 

 another, a radius, five metacarpals, three phalanges, a fibula, 

 and fragments of a scapula complete the list. The specimen 

 is No. 970 of the American Museum fossil reptilian collection. 



The Skull. 



The condition of the sutures, the fact that the rostral bone 

 had not ankylosed with the premaxillaries, and that the so- 

 called epoccipital bones, the lozenge-shaped ossicles around 

 the margin of the frill, were not sufficiently coossified with the 

 latter to prevent the loss of some of them, give evidence that 

 in spite of the enormous size of the animal it had not yet 

 reached maturity. The maxillary teeth have dropped out of 

 position with one exception, a tooth which lay deep in the 

 alveolar channel of the right side. Other teeth, found loose 

 in the matrix, were clearly of the upper series and are shown 

 in position in the photograph (Plate LIX). The rostral hone is 

 highly rugose, due to the impressions of blood-vessels over its 

 surface showing it to have been closely sheathed in horn. The 

 forward border is a full, gentle curve, while the inferior margin 

 is straight and nearly horizontal when the bone is in position, 

 as in most Testudinata. This, together with the form of the 

 predentary bone, which curves upward towards the tip, would 

 seem to indicate a cutting beak very turtle-like in aspect, as 

 one would be led to expect from somewhat similar feeding 

 habits, rather than the trenchant, downwardly curved, rap- 

 torial beak usually given to the restored Triceratops. The 

 fact that in Chelydra, where the upper beak is hooked, the bone 

 which supports it is of similar form, may be taken as corrobora- 

 tive evidence. 



