30 BULLETIN" 110, UNITED STATES NATIONAL MUSEUM. 



All of the premaxillae studied agree in having a constant number of five teeth, 

 which is two more than in Ceratosaurus, and one more than in Gorgosaurus and 

 Tyrannosaurus respectively. In the maxilla, however, the number appears to be 

 variable. ^Vll of those in the United States National Museum collections have 

 alveoli for 17 teeth, but a specimen (No. 666) in the American Museum of Natural 

 History, New York City, has only 15. One of the progressive specializations in this 

 group of carnivorous dinosaurs along with the reduction of the fore limb and foot, 

 appears to be a progressive decrease in the total number of teeth in the dental series, 

 as for example Antrodemus from the Morrison formation has 20 to 22 teeth in the 

 upper series and 15 in the lower; Gorgosaurus from the Belly River formation, 18 

 teeth in the upper and 14 in the lower series; and Tyrannosaurus from the Lance 

 formation has 16 teeth in the upper series and 13 to 14 in the lower. 



The premaxillary teeth are represented in specimen No. 4734, U.S.N.M., by 

 the second and fourth of the right side. The second is a large worn tooth about 

 to be shed, (fig. 10); the fourth a gerrd tooth, the point just emerging below the 

 parapet of the alveolus. The second is a hea\-y strong tooth with little lateral 

 compression that curves backward, being excellently adapted for use as a tearing 

 instrument. It is probably equalled if not exceeded in size by the first of the series. 

 Judging from the size of the alveoh the others progressively decrease in size toward 

 the back. 



The general features of the premaxillary teeth of Antrodemus are best displayed 

 in specimen No. 1890 Yale University Museum, shown here in figure 11. This spec- 

 imen was figured by Marsh as j^ertaining to Creosaurus atrox, but I am of the opinion, 

 as expressed on page 20, that in all probability it belongs to the genus Antrodemus. 



Material for study of the maxillary teeth is found in three specimens. No. 8423, 

 U.S.N.M., has the second, third, fourth, and fifth teeth almost perfectly preserved 

 in the right maxillary; No. 8335, U.S.N.M. has portions of the first, second, fourth, 

 sixth, seventh, eighth (young), ninth, tenth (entire), eleventh, twelfth, and thirteenth 

 (young) ; in the right maxillary. No. 4734, U.S.N.M., has the basal portion of the 

 ninth tooth in the left maxillary. In addition there are in the collection a great 

 number of detached teeth, but these are of little value, since at this time there is no 

 way to distinguish u])per from lower, and the location of loose teeth m the series 

 is a very uncertam undertaking. 



Apparently all of the teeth of Antrodemus have serrate edges. Tlie edges are 

 minute!}' serrated as m Ceratosaurus, there being about 10 denticulations in a 

 length of 5 mm. The teeth of the above genera appear to be indistinguishable. 

 These serrations are on both front and back borders, but the posterior continues 

 to the base of the tooth, whereas the anterior ends somewhat above it. 



From the front toward the back of the series the outer surfaces of the teeth are 

 gradually reduced, the inner expanded, until on the ninth or tenth tooth the two 

 surfaces are subequal. 



The anterior teeth are large, the fourth protruding 57 mm. below the parapet 

 of the alveolus. They continue robust back to the ninth, but posterior to that 

 tooth they decrease rapidly in size, the seventeenth, judgmg from the alveolus 

 being relatively of diminutive size. All of the maxillary teeth are latterly com- 



