92 BUIxLETIN 110, UNITED STATES NATIONAL MUSEUM. 



Hyoid. — Marsh says:' The hyoid bones appear to be four in number. They 

 are elongate, rod-hke bones, someM'hat curved, and in the present specimen were 

 found nearly in their original positions. 



The only evidence I find of the presence of bones of the hyoid arch is a small 

 section of a rounded rod-like bone attached by the matrix in an oblique position 

 from the vertical to the inner side of the right ramus, slightly in advance of the 

 articular. Both ends show fractured surfaces. There is a second and longer 

 flattened element held in the matrix parallel with and internal to the dentary of 

 the right side. Both of these bones may represent hyoid elements, but as to this 

 one can not be certain. 



TEETH. 



In the type skull of Ceratosaurus nasicornis the dental formula is as follows: 



Upper jaw: Premaxillary, 3; maxillary, 15; total, 18. 

 I/Ower jaw: Dentary, 15. 



Counting backward from the front of the jaws the following teeth are present 

 in the specimen: Eight maxillary, the second complete (displaced), and the root 

 of the fifteenth. Left maxillary, the second, fourth, sixth, eighth, ninth, tenth, 

 eleventh, twelfth, and thirteenth, roots of the fourteenth and fifteenth. Right 

 dentary, the sixth, twelfth, and thirteenth. Left dentary, the seventh, root of 

 the eighth, ninth, and tenth complete roots of the eleventh to the fifteenth inclusive. 

 There are three detached teeth lying in the matrix between the jaws, as shown in 

 figure 1, plate 17. All of the premaxillary teeth are missing. 



The maxillary series are compressed, recurved, teeth of robust size in front, 

 but from the ninth posteriorly gradually decreasing in size; the fourteenth and 

 fifteenth are both of relatively diminutive size. All display the serrate edges on 

 the anterior and posterior borders so characteristic of nearly all Theropoda. The 

 carinations are minutely serrated, there being about 10 denticulations in a space of 

 5 mm. The anterior carina passes gradually to the inner side of the cro-\vns of the 

 anterior half of the series, while the posterior carina follows a straight course well 

 toward the outer side of the crown. 



The great irregularity in size of contiguous teeth, to some extent, is due to the 

 different degrees of extrusion brought about by the loss of functional teeth at dif- 

 ferent times and their subsequent replacement by the growing germ teeth. Whether 

 the functional teeth are forced out at intervals by the continued development of 

 the germ teeth, or whether they are lost through accident, has not yet been de- 

 termined. It may be that both conditions prevail. 



The largest tooth preserved in this specimen is the fourth of the left maxillary, 

 which extends 70 mm. below the border of the socket, and is 27 mm. wide antero- 

 posteriorly at the base of the crown. 



The anterior maxillary teeth of Ceratosaurus appear to be more robust in their 

 proportions than in any individual of Antrodemus available for comparison at this 

 time, some of which apparently represent larger individuals. Except possibly this 

 difference in size, I have been unable to find characters that would enable one to 



' Dinosaurs of North America, 1896, p. 157. 



