168 DINOSAURS OF NORTH AMERICA. 



The scapula and coracoid of Apatosaurus, showu in PI. XIX, fig. 1, 

 are also characteristic features of the family they represent. The shaft 

 of the scapula is uot expanded above in any of the genera of the Atlan- 

 tosauridae, although this expansion is characteristic of the genus 

 Morosaurus and the family Morosaurida?, as shown in the same plate, 

 fig. 2. Another important difference is indicated on this plate, in the 

 coracoids, that of Apatosaurus being nearly square in outline, while in 

 Morosaurus and its allies the contour of the coracoid is subovate. 



BRONTOSAURTJS. 



The best-known genus of the Atlantosauridae is Brontosaurus, 

 described by the writer in 1879, the type specimen being a nearly 

 entire skeleton, by far the most complete of any of the Sauropoda yet 

 discovered. It was found in the Atlantosaurus beds', near Lake Como, 

 Wyoming, and the remains were nearly in the position in which they 

 were left at the death of the animal. This fortunate discovery has 

 done much to clear up many doubtful points in the structure of the 

 whole group Sauropoda, and the species Brontosaurus excelsus may be 

 taken as a typical form, especially of the family Atlautosauridaj. The 

 animal was about GO feet in length. A second species, equally gigantic, 

 has since been found in the same region. 



In PI. XX, fig. 1, a characteristic tooth of Brontosaurus is showu, 

 which may also be regarded as typical for the family. In fig. 2 of the 

 same plate the dentary bone is shown, with the teeth in outline. This 

 bone is one of the most characteristic of the whole skeleton, as will be 

 seen by comparing it with tbe corresponding parts of other Sauropoda 

 represented in the following plates. 



The genus Brontosaurus may be readily distinguished from all the 

 other Sauropoda by the sacrum, which is composed of five anchylosed 

 vertebra?, none of the other genera in this group having more than four. 

 The sternum, moreover, consists of two separate boues, which are 

 parial, and were united to each other on the median line apparently 

 by cartilage only. In several other respects the genus resembles 

 Morosaurus. 



The present species, aside from its immense size, is distinguished by 

 the peculiar lightness of its vertebral column, the cervical, dorsal, and 

 sacral vertebra? all having very large cavities in their centra. The 

 first three caudals, also, are lightened by excavations in their sides, a 

 feature first seen in this genus, and one not observed in the other 

 families of this group. 



THE SCAPULAR ARCH. 



The scapular arch in the present species is, fortunately, better known 

 than that of any other member of the present order. In PI. XXII the 

 various bones are represented in position, and in fig. 2 of the same plate 

 a sternal bone is showu separately. The scapula resembles in general 

 form the corresponding bone iu Apatosaurus, but the shaft is longer 

 and the upper end somewhat wider. 



