For nearly half a century geologists have followed with great interest and admiration the discoveries of fossil vertebrate animals in the west of North America. From the early days when western pioneers brought back scattered fragments for study by Leidy, to the seventies and eighties of last century when Cope and Marsh led or encouraged adventurous expeditions to collect fossils in the territories then occupied by hostile Indians, the continual succession of new forms of extinct reptiles, birds, and mammals met with in an unusual state of preservation, excited increasing attention. So remarkable, indeed, were these finds and so sporting was their pursuit, that rivalries arose and passed beyond the state of friendly emulation which is good for real progress. It was thus fortunate for American palæontology that a younger generation of well-trained enthusiastic students was then ready to enter the field, and especially fortunate that their leaders were imbued with a harmonious spirit of co-operation. Among these leaders was the subject of our present biographical sketch, who has perhaps done most by his personal influence to maintain the happy relations which now exist between all workers in vertebrate palæontology in America.