246 FIELD COLUMBIAN MUSEUM. 
series. Together with this arrangement we find a more generalized 
structure of the zygapophyses and hyposphene, such as was noticed 
in Morosaurus. The former are moderately broad, but are nowhere 
placed far apart; the latter has a slightly greater development than 
in the above-mentioned genus. In Brachiosaurus, the zygapophyses 
reach the extreme reduction and the hyposphene-hypantrum 
articulation reaches the extreme development. The zygapophyses 
are crowded together near the median line in a way which would render 
impossible any considerable lateral movement of the body. The 
hyposphene articulation is well constructed to prevent lateral dis- 
placement. The strong thoracic ribs with widely divergent head and 
tubercle firmly anchored in the same horizontal plane doubtless 
added greatly to the strength of the vertebral column in this region. 
In this we recognize the rigid quadrupedal structure of the vertebral 
column. : | 
From the above considerations it will be seen that Brachiosaurus 
is the culminating type of a phylum, distinct from anything hitherto 
known in America. Its length of limb and bodily proportions show 
that it was fitted for purely quadrupedal movements. Though the 
structure of the feet and lower legs is unknown, there is every reason 
for believing that the animal was specialized in terrestrial habits. 
This fact would restrict its range to grounds where conditions were 
less favorable for its preservation and so account for its remaining so 
long undiscovered. 
‘ SUMMARY. 
The following conclusions are reached in this paper: 
1. The genus Brachiosaurus, together with the smaller related 
form, Haplocanthosaurus, should be placed in a new family of the 
opisthoccelia for which the name Bracluosauride is here proposed. 
2. The distinguishing characters of this family, so far as known, 
are: Humerus as long as femur; neural spines of the vertebre simple; 
dorsal vertebree numbering more than ten. 
3. Brachiosaurus is a highly specialized form, related to, but not 
directly descending from, Haplocanthosaurus. 
4. The known characters which distinguish Brachiosaurus are: 
Its large size, immense thorax, highly specialized hyposphene-hypan- 
trum articulation of the vertebre, low, broad structure of the verte- 
bral pedicles, and the unusual breadth of the sacrum. 
5. While Morosaurus, Apatosaurus, and Diplodocus are, by reason 
of their elevated sacral spines and strong dorsal vertebre, fitted for 
assuming the upright position, the short sacral spines and heavy fore 
