180 DINOSAURS OF NORTH AMERICA. 



of five immature teeth, in various stages of development, preparing to 

 take its place. These snccessional teeth are lodged in a large cavity, 

 which extends through the whole dental portion of the maxillary. The 

 succession is also similar in the premaxillary teeth and in those of the 

 lower jaws. 



THK VKKTEBE*. 



The vertebral column of Diplodocus, so far as at present known, may 

 be readily distinguished from that of the other Sauropoda by both the 

 centra and chevrons of the caudals. The former are elongated and 

 deeply excavated below, as shown in PI. XXVI, figs. 4 and 5. The 

 chevrons are especially characteristic, and to their peculiar form the 

 generic name Diplodocus refers. They are double, having both anterior 

 and posterior branches, and the typical forms are represented in figs. 6 

 and 7 of the above plate. 



The cervical and dorsal vertebra' of Diplodocus are represented by 

 typical examples on PI. XXVI, fig. 3, and PI. XXVII, and the sacrum 

 with ilium attached is shown on PI. XXVIII. 



THE STERNAL BONES. 



The sternal bones in Diplodocus are especially large, and in form 

 resemble those in Brontosaurus excelsus. Those in Brontosaurus amplus 

 are less robust, and are somewhat similar in shape to those of Moro- 

 saurus, as shown in figs. 29 and 30. 



THE PELVIC GIKDLE. 



A most characteristic bone of the two families of Sauropoda first 

 described is the ischium. In the Atlantosaurida? the ischia are mas- 

 sive and directed downward, with their expanded extremities meeting 

 on the median line. In the Morosaurida^ the ischia are slender, with 

 the shaft twisted about 90°, directed backward, and the sides meeting 

 on the median line, thus approaching this part in the more specialized 

 dinosaurs. The ischia referred to the genus Diplodocus (PI. XXVIII, 

 fig. 3) are intermediate in form and position between those above men- 

 tioned. The shaft is not expanded distally, nor twisted, but was 

 directed downward and backward, with the sides meeting on the 

 median line. 



The feet of Diplodocus are shown in Pis. XXVIII and XXIX. 



SIZE AND HABITS. 



The type specimen of Diplodocus, to which the skull here figured 

 belongs, indicates an animal intermediate in size between Atlanto- 

 saurus and Morosaurus, probably 40 or 50 feet in length when alive. 

 The teeth show that it was herbivorous, and the food was probably 

 succulent vegetation. The position of the external uares would seem 

 to indicate in some measure an aquatic life. 



