188 FIELD COLUMBIAN MUSEUM. 
ing from the American Museum specimen No. 222, described by him 
as Camarasaurus. In this he has evidently fallen into error from mis- 
taking sacral v for caudal 1 and from comparing the caudal series of 
this form with that of Diplodocus. (See Figs. 11 and 12, Plate xvii.) 
As neither of the three caudal series above mentioned is complete 
distally they offer no positive basis of comparison as to nuinber of 
vertebre. In the Museum specimen the number of anterior caudals 
bearing ribs is twelve, that figured in the Yale specimen is the same, 
while the number observed by the writer in the American Museum 
specimen (exclusive of sacral v) is eleven. The diapophyses disap- 
pear in the Museum specimen and in the Yale specimen in caudal v; 
in the American Museum specimen they disappear in caudaltv. The 
number of anterior vertebrz having lateral cavities in the centra is five 
in the Museum specimen as compared with three described by Marsh 
in the Yale speciinen. While the point of disappearance of sucha 
vestigial element as the caudal rib cannot be regarded as constant, 
and the presence of lateral cavities in the centra is even more variable, 
the fact that these points in Marsh’s restoration agree so closely with 
the Museum specimen indicates that the restoration is approximately 
correct in this particular. On the other hand, there is probably not 
more than one anterior caudal vertebra missing from the series in the 
American Museum specimen. | 
The frst caudal vertebra has a number of characteristics which at 
once distinguish it from other members of the series. Most noticeable 
among these is the anterior articulating surface of the centrum, which 
is concave in its upper half, but convex below. The interior of the 
centrum contains numerous small cavities, the pedicles are hollow, the 
base of the spine is complicated by numerous infoldings of the periph- 
eral lamina, the sacral ribs are‘expanded into broad, lateral wings 
codssified with the diapophyses by a thin vertical plate thickened and 
rugose at its lateral border; the prezygapophyses face upward as well 
as inward, and are excavated at their bases by deep lateral fosse. 
Each of the anterior caudal vertebre bears a pair of lateral plates 
which project from the surface of the centrum, the neural arch, and 
the base of the spine. These are made up of two elements: (1) the 
caudal rib, which arises from the lateral surface of the centrum, and 
(2) the diapophysis, which springs from the neural arch as in the sacral 
and presacral vertebre. These elements are very similar in form to 
those of the primary sacrals, except that they are connected by a con- 
tinuous vertical plate which is thickened at its lateral border, ie 
a stout bar. (Plate 11.) 
The caudal rib springs from the lateral surface of the centrum, 
