42 MEMOIRS OF THE CARNEGIE MUSEUM 



here, except to note that the cervical ribs in Nos. 84 and 94 are much smaller in 

 comparison with the size of the vertebrse than are those figured by Marsh in his 

 description of D. longus. 



The free or articulating ribs of the dorsal region are ten in number on either side. 

 Of these eighteen are preserved in No. 84 and those of the right side are essentially 

 complete, save the second, which is wanting in the right series but present in the left, 

 though the extreme distal end and the capitulum and tuberculum are wanting. 



The first rib differs from all the others in being triangular in cross section 

 throughout its entire length, except for a short distance just beyond the union of 

 the capitulum and tuberculum. It diminishes regularly but very gradually in size 

 from the point of union of the capitulum and tuberculum to the distal extremity. 

 The latter is triangular in cross section and pointed, without any indication of the 

 distal expansion commonly seen in the first rib of the larger mammalia. The ex- 

 ternal surface of this rib is rather broad proximally and is produced posteriorly into 

 a rather stout blade and anteriorly into a somewhat shorter projection, so that in 

 this region a cross-section of this rib would be T-shaped with one arm more ab- 

 breviated than the other. The capitulum and tuberculum are small, subequal, and 

 supported by peduncles of about equal length, though the tubercular process is 

 slightly longer and stronger than the capitular. 



The second rib is wanting in the right series, but is represented in the left, though 

 lacking the extremity and the capitulum and tuberculum. The external surface is 

 broad and rather fiat throughout the entire length. The inner surface is deeply 

 convex throughout the greater part of the length of the rib, but toward the ex- 

 tremity it becomes gradually flattened, resulting in a thin, flat, spatulate extremity 

 contrasting strongly with the triangular pointed extremity of the preceding rib. 



The third rib like the first is quite complete. The tuberculum and capitulum 

 are each pedunculate, compressed and subequal in area,* while their supporting proc- 

 esses are about equal in length. The external surface is broad proximally, some- 

 what contracted medially, and slightly expanded distally, where the anterior edge 

 is produced into a sharp ridge. The inner surface is convex. In cross section it is 

 somewhat elliptical throughout the greater portion of its length, but proximally it 

 is T-shaped, with the outer surface forming the top of the T. 



The fourth rib is complete. The head and tuberosity of this rib are the largest 

 of any in the series. They are borne at the extremities of their respective proc- 

 esses, and the capitular process is somewhat longer and more slender than the tuber- 

 cular. This rib is triangular in cross section proximally but much flattened distally. 



The fifth rib is in general form like the fourth. It is slightly longer and the 



