The collection which has been of the greatest value is that at the American Museum of Natural History, chiefly assembled by Dr. J. S. Newberry from the dumps of the coal mines at Linton, Ohio, while he was in charge of the Ohio Geological Survey (1869-1884). This collection, a part of which is at Columbia University, furnished Cope with the most of his type material for the "Synopsis of the Extinct Batrachia from the Coal Measures" (123).[A] This entire collection, including all of Professor Cope's types and representing many new and hitherto undescribed forms, was generously placed at the writer's disposal for a period of five years through the kindness of Dr. Bashford Dean and Dr. Louis Hussakof. Dr. Hussakof made a trip through the Linton region and his description of the place occupied by the "Old Diamond Mine" is given on page 16. [Footnote A: The numbers in parentheses refer to the bibliography at the end of this volume.] An interesting collection of air-breathing vertebrates from the Coal Measures, representing 19 species, is in the U. S. National Museum (464). This is chiefly the collection of Mr. R. D. Lacoe and includes specimens from Mazon Creek, Illinois, from Kansas, and from Linton, Ohio. It is especially important in that it contains the skeleton (plate 20, fig. 3) of _the oldest known reptile_, _Eosaurus copei_ Williston (Jour. Geol., XVI, 295). It contains also, besides many of Cope's types, new forms which have been described by the writer (464, 470, 471, 472, 473, 474, 478, 479). Dr. Stuart Weller first secured the use of this collection for me, and its continued use has been granted by Dr. C. D. Walcott. Mr. Charles Gilmore has called my attention to several interesting specimens and has kindly loaned them for description. 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).