STRUCTURE AND RELATIONSHIPS OF OPISTHOCCELIAN 
DINOSAURS. 
PART Il. 
THE BRACHIOSAURID-. 
BYE. you RGAE. 

The genus Brachiosaurus was recently described* by the writer 
from the humerus, femur, coracoid, and such parts of the sacrum and 
vertebral centra as could be seen before the specimen had been 
removed from the matrix. During the past winter the sacral and 
presacral vertebre, which had been badly damaged by weathering, 
have been reconstructed with great care and patience by Messrs. J. 
B. Abbott and C. T. Kline. As these parts have one after another 
been worked out, the unusual character of this animal, which was 
first indicated by the extraordinary proportions of the humerus, has 
become more and more evident. So different is its structure from 
that of other members of the Opisthoccelia that the writer feels 
justified in placingitin anewfamily. The Brachiosauride ts, there- 
fore, proposed as a family group, to include this genus together with 
the smaller and more primitive form recently described by Hatcher 
under the name Haplocanthosaurus. 
The family characters so far observed are: Humerus as long as 
femur; neural spines of vertebre simple; dorsal vertebre more than ten. 
Other characters equally distinctive will doubtless develop as 
these animals become better known. The following key will aid in 
determining members of this group: 
Opisthocelian dinosaurs with fore leg longer than hind; vertebral 
spines simple throughout; number of dorsal vertebre more than ten: 
Family Brachiosaunde. 
(a) Size medium, dorsal vertebre fourteen; centra not elongate; neural 
arch unusually elevated, diapophyses directed obliquely upward and out- 
ward, hyposphene-hypantrum articulation moderately developed: Genus - 
Haplocanthosaurus. 
(b) Size large; neural arches not unusually elevated, spines increas- 
ang in length from sacrum to mid-dorsal region, hyposphene-hypantrum 
* Am. Jour. Sci., Ser. 4, vol. 15, p. 200. 
229 
