10 BULLETIN 16 9, UNITED STATES NATIONAL MUSEUM 



particular institution. In 1908 he had worked principally in the 

 Silberling Quarry. In 1909 Gidley visited the field and then opened 

 the Gidley Quarry at a site, Loc. 4, previously discovered by Silberling. 

 Gidley himself collected many fine specimens here, and the work was 

 continued by Silberling in 1909-11, and later, along with repeated 

 prospecting of surface localities. In 1911 Gidley made another visit 

 to the field.^ 



In 1909 Gidley described the splendid skull, jaws, and partial skele- 

 ton of Ptilodus that had been found in 1908 by Silberiing in the Silber- 

 ling Quarry. This is still the best multituberculate specimen in any 

 museum, and the best single mammal specimen ever found in this 

 field. Gidley continued the preparation of the collection, work done 

 entirely by himself, as time and other duties permitted. Tliis was 

 completed in 1920. In the meantime two preliminary papers had been 

 pubhshed, one on Myrmecoboides (Gidley, 1915) and one on the clae- 

 nodonts (Gidley, 1919). After the whole collection was prepared he 

 began monographing it, but only the section on the Primates (Gidley, 

 1923) was completed or published. The extent of his unpubUshed 

 work has already been noted. 



In 1930 Silberling made a renewed examination of the field and also 

 reopened the Gidley Quarry and made a collection that was purchased 

 by the American Museum. In 1932, under the auspices of the Na- 

 tional Museum (with the donation of my services by the American 

 Museum), Silberling and I went over the whole area and adjacent 

 regions, with the present work in mind. We then made the map 

 (pi. 1) that accompanies this memoir and also made detailed strati- 

 graphic observations. A small amount of material was collected, 

 incidental to our visits to all the fossil localities, but no intensive 

 collecting or quarrying was undertaken. 



In 1935 the Third Scarritt Expedition of the American Museum, 

 consisting of Mr. Silberling, a camp man, and me for the entire season, 

 and Mr. and Mrs. Fenley Hunter, Dr. Walter Granger, and Albert 

 Thomson for shorter periods, spent four months in tliis field, pros- 

 pecting most of the surface localities, reopening the Gidley and Silber- 

 hng Quarries, and developing a new quarry, named the Scarritt 

 Quarry. The resulting collection, about equal in size to that here 

 described, is in the American Museum. The material from the Scar- 

 ritt Quarry has been described (Simpson, 1936b), and the results are 

 here included in the general sections but not in the detailed descrip- 

 tions. The surface material, wliich is relatively abundant and im- 

 portant but does not include any species not also present in the 

 National Museum collection, has also been identified and is mentioned 

 where apropos in the present work. The very large Gidley Quarry 



' Gidley's statement (1923, p. 1) that he visited the field in 1008 and 1909 is probably a misprint, for it is 

 contrary to Silberling's memory and to letters and other records that seem to show that his visits were in 

 1909 and 1911. 



