16 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 81 



second and third caudals is designated the third. Thus numbered, 

 the fourth, sixteenth, eighteenth, nineteenth, twentieth, and twenty- 

 first were found articulated. From these fixed points the other 

 more or less scattered elements have been allocated. 



A large chevron bone found near the proximal caudals was at 

 first thought to belong to the present specimen, but its very large 

 size with an open haemal canal was not in accord with the known 

 chevron of this region in Dlplodocus^ and it therefore has been 

 omitted from the skeleton. 



The twelfth chevron, arbitrarily placed in the series, is unlike any 

 known chevron of Diplodocus either in shape or position in the 

 series, but its occurrence in relation to the tail and its general 

 features both suggest relationship with the present specimen. This 

 bone is open above the haemal arch, expanded at its base with an 

 elongated extension that turns posteriorly nearly at right angles 

 to the articular portion. In the specimen described by Osborn all 

 chevrons are closed above the haemal canal as far posterior as the 

 thirteenth chevron. With the few exceptions briefly discussed, all 

 the other chevron bones are in accord with previously known 

 specimens, which have been fully described by Osborn and Hatcher. 



Rihs. — Of the 20 thoracic ribs that form the complete series in 

 Dij^tJodocus^ 10 are preserved in the present specimen. The first is 

 missine: from the left side, but the other nine were found articulated 

 with their respective vertebrae. The remaining rib, the third of 

 the right side, was found disarticulated but not far removed from 

 the vertebral column. The ninth and tenth ribs were fully coalesced 

 with the diapoi:)hyses of the vertebrae and the eighth partially so, 

 thus giving additional evidence of the senile character of the indi- 

 vidual. Riggs ^* has observed a somewhat similar condition in 

 Apatosaurus in that the last rib was fully ankylosed w^ith the 

 transverse process. 



The ribs, except for the loss of minor portions, are in a splendid 

 state of preservation, and having suffered but little distortion from 

 post-mortem causes they display for the first time the true shape 

 of the thorax. 



The ribs as articulated differ from previous reconstructions in 

 two important particulars — first, a decided backward sweep of the 

 lower portion of the shafts of the third and fourth ; and second, the 

 strong inward curvature of the distal portion of the posterior mem- 

 bers of the series. In both of these respects they are in striking 

 contrast to the more or less straight ribs in the Diplodocus carnegii 

 skeleton in Pittsburgh. Critical examination of the plaster ribs 



2* Field Columbian Mus. Publ. 82, vol. 2, p. 177, 1903. 



