HATCHER : DIPLODOCUS (mARSH) 3 



It is only by encouraging the collecting and investigation of the remains of these 

 extinct and gigantic reptiles in as many institutions as possible, and by combining 

 the results of all, that we may hope eventually to be able to trace the phylogeny of 

 the different genera of Dinosaurs, in respect to the nature of which we are as yet 

 quite ignorant. 



The obstacles to a systematic study of the Dinosauria just enumerated serve only 

 to increase the importance of the discovery of any additional information regarding 

 the structure and affinities of the different genera, and to render desirable the early 

 publication of such information. This is especially true when, as in the present 

 case, recent discoveries have brought to light many important and hitherto unknown 

 skeletal features and made it possible to describe, almost in its entirety, the osteology 

 of an animal belonging to a genus, Avhich is representative of a great and highly in- 

 teresting suborder, as yet known only from fragmentary skeletons of different indi- 

 viduals, which for the most part pertain to different genera and species. 



The material upon which the present paper is based belongs for the most part to 

 one of two skeletons (Nos. 84 and 9i)} The former skeleton was collected by Dr. 

 J. L. Wortman and party during the expedition of 1899, while the latter was secured 

 by Mr. O. A. Peterson and his assistants during the expedition of 1900, while en- 

 gaged in making further excavations in the same quarry on Sheep Creek, in Albany 

 County, Wyoming, which had yielded Dr. Wortman such excellent material during 

 the previous season. Aside from these two skeletons o£ Diplodocus this quarry, or bone 

 deposit,^ has furnished a skull and considerable portion of the skeleton of Stegoscmrus 

 as well as a great part of the skeletons of Brontosaurus and numerous remains of 

 other Dinosaurs as yet undetermined. 



For all this, and much other valuable material, brought together by the expedi- 

 tion of 1899 conducted by Dr. Wortman and those of 1900 carried on by Mr. Peter- 

 son under the direction of the present writer, we are indebted to the well-known 

 generosity of Mr. Andrew Carnegie, the founder of this institution. 



The work of freeing the bones from the matrix and preparing them for stud}^ has 

 been carried on under the immediate direction of Mr. A. S. Coggeshall, chief pre- 

 parator in the paleontological laborator3^ In this work Mr. Coggeshall has shown 

 exceptional skill and patience. He has been assisted by Mr. Louis S. Coggeshall 

 and Mr. A. W. Vankirk, and in the winter months especially, by Mr. 0. A. Peter- 

 son, the well-known collector as well as skilled preparator of vertebrate fossils. 



1 The numbers in this paper refer to the Department numbers in the Card Catalogue of Vertebrate Fos- 

 sils in the Carnegie Musevim. 



2 Known as Quai'ry D on field labels and notebooks. 



