A small but interesting collection of Mazon Creek Amphibia is that of the Peabody Museum of Yale University. Through the courtesy of the officers of this museum the writer was permitted to study these specimens and was given a grant for their illustration. The results of that study are contained in a previous paper ([478]) and in the present memoir. Dr. Schuchert has offered suggestions as to the environmental conditions of the ancient Amphibia.
A few specimens of Coal Measures Amphibia are at the Walker Museum, University of Chicago. This collection includes the type of Micrerpeton caudatum Moodie, the first branchiosaur discovered in the western hemisphere, and a few specimens from Linton, Ohio.
A single specimen of Amphibamus grandiceps Cope, very beautifully preserved, is in the possession of Mr. L. E. Daniels, of Rolling Prairie, Indiana. This specimen has been studied and described by Hay ([316]) and by the writer ([462], [469], [478]).
The works of Cope and Dawson, published between 1860 and 1897, on the Amphibia from the Coal Measures, have been indispensable in the present study. It has been necessary to rely on the published descriptions and photographs of the interesting fauna from Nova Scotia, since it has not been possible for me to visit and examine the types preserved in the Peter Redpath Museum of McGill University and in the British Museum of Natural History. It has been possible to check Dawson's work, to a certain extent, by a study of a series of excellent photographs of the types of Coal Measures Amphibia collected by Dawson and Lyell and described by Dawson and Owen. The descriptions of these authors have been drawn on for the discussion of the Canadian forms.
The descriptions given below have been made full and complete in the belief that in this way our knowledge of these interesting vertebrates may be advanced. Many of the species have been described elsewhere in scattered papers by various authors. These descriptions have been revised and verified and are collected here in monographic form. The work is a morphologic and taxonomic revision of the Amphibia from the Coal Measures of North America. Especial attention has been paid to the factors which have been most active in the evolution of the group, so far as these factors may be interpreted. It is the author's hope that this review may open up the field for many more workers, since we are just beginning to learn about the evolution of this group of vertebrates.
The trustees of the Elizabeth Thompson Science Fund allotted a grant for the present investigation. This aid has enabled the writer to present his work in much better form than would have been possible otherwise. Dr. S. W. Williston has offered many suggestions and criticisms which have been gratefully adopted. It is with the greatest sense of pleasure that the author dedicates this memoir to his teacher and friend. After the manuscript was completed the author enjoyed a visit from Mr. D. M. S. Watson, of King's College, London, whose knowledge of the European and African forms enabled him to offer several very valuable suggestions.
It is fitting also to express my indebtedness to the Carnegie Institution of Washington for the privilege of publishing my work in the series of monographs contributed by Dr. E. C. Case, dealing with the anatomy and relationships of the early land vertebrates of North America.
Roy Lee Moodie.