196 FIELD COLUMBIAN MUSEUM. 
SUMMARY. 
The following conclusions are derived from this paper. 
1. ‘‘Opisthoceelia’’.has precedence over ‘‘Sauropoda’’ and ‘‘Ce- 
tiosauria.”’ 
2. Brontosaurus is a synonym of Apatosaurus. 
3. The species A. ajax cannot be recognized in the adult; A. ex- 
celsus is probably a synonym of A. laticollis; A. amplus is valid. 
4. The number of dorsal vertebre is ten. 
5. Llhere are no lumbar vertebre. 
6. There are five pairs of true, and five pairs of floating ribs. 
7. The sacrum is made up of three primary and two secondary 
sacral vertebre, all of which, in the adult, connect with the ilia by 
sacral ribs and diapophyses. The primary sacrals are codssified by 
their centra, zygapophyses, and spines; the secondary sacrals are free 
until adult age and then codssify with the true sacrals by centra and 
zy gapophyses. 
8. Sacral 1 is a modified dorsal, sacral v a modified caudal. 
9g. The last pair of floating ribs tends to codssify with the vertebra 
by head and tubercle, and with the ilia by the distal ends. 
to. There are one or two more anterior caudal vertebre than was 
figured in Marsh’s restoration. 
tz. The caudal chevrons pass from the closed y anteriorly to the 
double-arch type posteriorly very much as in Dzplodocus. 
12. The ilium inclines more forward, and the pubis and ischium 
are more divergent distally than previously figured. 
13. The crest of the dorsal arch is at the anterior end of the 
sacrum. 
