170 FIELD COLUMBIAN MUSEUM. 
coracoid, and sacrum, and these parts were figured.* In December of 
the same year the genus 4rontosaurus was proposed upon an unusually 
complete specimen briefly described.f Later a more complete descrip- 
tion was given and a number of parts figured.{ Two different restora- 
tions were later published.§ : 
The genus 4rontosaurus was based chiefly upon the structure of 
the scapula and the presence of five vertebre in the sacrum. After 
examining the type specimens of these genera, and making a careful 
study of the unusually well-preserved specimen described in this:paper, 
the writer is convinced that the Apatosaur specimen is merely a young 
animal of the form represented in the adult by the Brontosaur speci- 
men. As before pointed out, | the imperfectly ossified condition of the 
scapula, coracoid, and sacrum indicates a young animal. (Figs. 1 and 
2.) The presence of but three coalesced vertebre in the sacrum points 
to the same conclusion as will appear from a comparative study of sacra 
offered in this paper. The proportionate size of the two specimens, the 
shorter shaft and narrow distal end of the scapula, the outline of the 
coracoid, the open chevrons, the form of the anterior thoracic and the 
cervical vertebre, and the structure of the pelvis (Figs. 3 and 4) all dis- 
play such similarity as one would expect in a young animal of the Bron- 
tosaur type. In fact, upon the one occasion in which Professor Marsh 
compared 4] these two genera he mentioned the similarity between the 
scapule of their respective types. In view of these facts the two 
genera may be regarded as synonymous. As the term ‘‘Apatosaurus’’ 
has priority, “‘Brontosaurus’’ will be regarded as a synonym. 
The following species have been referred to this genus: 
A. ajax Marsh, type of genus, Am. Jour. Sc.,. (3); xiv, 514 eames 
1877. 
A. grandis Marsh, ibid., (3), xiv, 515, Dec., 1877. 
Referred to AMorosaurus, ibid., (3), xvi, 414, Nov., 1878. 
A. laticollis Marsh, ibid., (3), xvii, 88, Jan., 1879. 
A. excelsis Marsh, ibid., (3), xvii, 503, Dec., 1879. 
(Brontosaurus excelsus) this paper. 
A. amplus Marsh, ibid., (3), xxi, 421, May, 1881. 
Of this number probably not more than two species are valid. 
A. ajax is based upon a specimen too young to admit of specific de- 
termination. <A. grandis is a synonym. A. J/aticollis was described 
* Tbid., Vol. xvi, p. 86. 
t Ibid., 3d Ser., Vol. xviii, p. Sor. 
f Ibid., 3d Ser., Vol. xxi, p. 417-21. 
§ Ibid., 3d Ser., Vol. xxvi, Pl. 1; The Dinosaurs of North America, Pl. xLut. 
|| Am. Jour. Sc., 4th Ser., Vol. xv, p. 305. 
§| The Dinosaurs of North America, U.S. Geolog. Surv., Vol. xvi, p. 168. 
