144 Annals of the Carnegie Museum. 



to refrain from further remarks as to the nature of the skull of Apato- 

 satirus, in the hope that more light may be soon thrown upon the 

 subject. 



It should be stated that the writer has in preparation a large mono- 

 graphic paper relating to the genus, based in part upon the speci- 

 men specifically described in this paper, the publication of which 

 has been held back, partly in order that the plates and illustrations 

 which are to accompany it may be prepared. 



Apatosaurus louisae, sp. nov. 



Type: No. 3018, Carnegie Museum Catalog of Fossil Vertebrates. 

 Locality: Carnegie Quarry, near Jensen, Uinta County, Utah. 

 Horizon: Upper Jurassic (Morrison Beds). 



The differences between the present species and Apatosaurus 

 (Brontosaurus) excelsus, which reveal themselves in many of the minor 

 details of structure, such as the position and form of the laminae 

 supporting the transverse processes of the dorsal vertebrae, are 

 multitudinous, but may perhaps in part be attributed to individual 

 variation. Of these differences I shall not speak in the present paper. 

 A few of the specific characters which will facilitate the recognition 

 of the species are the following: 



1. The lateral cavities in the centra of the dorsals do not have their 

 openings situated at the middle of the centrum, as in A. excelsus, 

 but they are located higher up, at the base of the pedicle of the 

 neural arch, and open inwardly and downward, forming deep pocket- 

 like cavities. 



2. The round hemispherical articulating surface of the anterior 

 ends of the centra, which are well-developed in the first five dorsal 

 vertebrae of A. excelsus, appear only in the first two dorsals of A. 

 louisce, being feebly indicated in dorsal No. 3, after which all the centra 

 in A. louisce have their anterior articulating surfaces platyan. 



3. Whereas in A. excelsus Marsh, and in another specimen belonging 

 to the Carnegie Museum, referred to excelsus by Hatcher, and coming 

 from the same horizon in Wyoming from which Professor Marsh 

 obtained the type, there is a large foramen piercing the lateral trans- 

 verse laminae on either side of the anterior three caudals above the 

 level of the neural canal, such openings do not occur in the type speci- 

 men of A. louisce. This causes the bones to present a very difTerent 

 appearance from those of the type of A. excelsus when viewed either 

 from before or behind. • 



