Maryland Geological Survey 191 



closely that of lironiosaurus, being much lighter and less deep than that of 

 Moro.munis. Anteriorly, it is rounded and abruptly truncated at the 

 symphysis. On the ventral aspect is the open meckelian groove, begin- 

 ning at the symphysis and sweeping backward to the extreme end. About 

 the mid-length of the bone this groove widens out to form the man- 

 dibular fossa, its outer margin extending downward to form a thin, 

 curved plate of bone which forms at least one-half of the outer surface of 

 the jaw. The meckelian groove is not present in the anterior half of 

 the jaw of Brontosaurus, though in Morosaurus grandis it is very similar, 

 both in position and in extent. There seem to have been at least thirteen 

 teeth in commission at one time, and none of the crowns now visible in 

 the alveoli have the spoon-like shape. 



DIMENSIONS 



Length of dentary (tangential) 122.0 mm. 



Depth at anterior end 30.5 mm. 



Depth at posterior end (estimated) 50.0 mm. 



Thickness at 3d alveolus 15.0 mm. 



The maxillary (pi. xiv, fig. 6) resembles that of Morosaurus rather than 

 of Brontosaurus, especially in its anterior portion, as the upward process 

 for articulation with the prefrontal, while wanting, seems to have had 

 its origin much further forward than in Brontosaurus, indicating a short, 

 high skull, like that of Morosaurus. In proportion of thickness to 

 length, the present maxilla again resembles the more robust Morosaurus 

 rather than Brontosaurus. The number of alveoli in Morosaurus is nine, 

 and in Pleurocoslus nine or ten as compared with thirteen in Bronto- 

 saurus. There is, as usual, a corresponding row of foramina on the 

 inner face, opening into a shallow groove. 



The dimensions of the left maxilla (No, 5667, U. S. ISTational Mu- 

 seum) are as follows : 



Length to mx.-pmx. facet 88. 5 mm. 



Length of tooth series 71.0 mm. 



Thickness 15.5 mm. 



The alisphenoid (pi. xvi, fig. 1) (No. 5668, U. S. National Museum) re- 

 sembles very closely the corresponding bone of Morosaurus, though dif- 

 fering somewhat in proportions, being more broadly expanded superiorly. 

 13 



