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172 FIELD COLUMBIAN MUSEUM. 
from a single cervical vertebra which may or may not be identical with 
the type species. A. exce/sus is familiar as the type of ‘‘Brontosaurus,”’ 
and is based upon a large part of a skeleton. ‘The sixth and the 
last cervical vertebre of this specimen as figured by Marsh* show 
such a similarity to the type of A. /aticollis as to indicate that the 
intervening ninth or tenth vertebra would prove identical. How- 
ever, the present knowledge of the cervical series does not admit of 
positive identification. A. amplus has not been figured and cannot 
now be determined. The Museum specimen will be regarded as con- 
specific with the well known Yale specimen and designated as Afato- 
saurus excelsus. . 
The genus Apatosaurus may be distinguished from other members 
of the Opisthoceelia by the following characteristics: Scapula with 
shaft and spine almost at right angles; shaft long and slender with 
slightly expanded distal end; ischium with acetabular surface at right 
angle to shaft and distal end expanded; sacrum in adult specimens 
with five ilium-supporting vertebre; anterior dorsal spines paired, 
long, and slender; anterior caudal centra with lateral cavities. 
DESCRIPTION OF SKELETON. 
DorsaAL VERTEBRA. (Plates xtvi1 and tu.) The vertebre lying 
between the cervical and the sacral regions are all rib-bearing, and 
hence may be designated by the term ‘‘dorsal’’; but in the following 
description they will be referred to as ‘‘presacral’’ and numbered from 
the sacrum forward in order to afford a definite basis of reckoning, 
since the fragmentary condition of presacral x1 does not admit of its 
position in the series being determined with absolute certainty. 
However, there is every reason to believe that this vertebra is the last 
cervical. 
The dorsal vertebre are of the opisthoccelous type, and are all rib- 
bearing. So much may be said of them as a group—as to other char- 
acteristics they represent a continuous transition, passing from the 
elevated and slender type posteriorly to the depressed and wide-armed 
type of the anterior dorsal region. In view of this wide difference 
between the anterior and posterior extremes of the series, it is not sur- 
prising that isolated vertebre have been made the types of three or 
more different genera. Variation between the extreme types of the 
dorsal series is especially noticeable in the following four vertebral 
elements. (1) The centra, (2) the neural spines, (3) the transverse 
processes, and (4) the capitular facets. In order to bring out their 
* Plates XxX and xx1, the Dinosaurs of North America. 
