Ordinary mucilage may be used for mounting drawings and photographs, but photo paste gives good results and is perhaps cleaner to handle. Dry-mounting tissue is well adapted to mounting single illustrations but not groups of figures. Liquid rubber is sometimes used, but it is not suitable for mounting small figures, such as drawings and photographs of fossils. It can be used satisfactorily for mounting temporary plates and for mounting photographs in albums and on large cards for study or exhibition; but it has not proved to be a permanent adhesive. Its special merit is that it does not cause either the photograph or the mounting sheet to warp. It is applied by spreading it evenly over the back of the photograph with the fingers. The superfluous rubber can easily be removed from the hands and from the cards or sheets when it is dry. Anything mounted with liquid rubber can be easily removed. If a plate is to be made up of a small number of figures that require different reductions, the author, instead of mounting or pasting the separate figures on one card in the manner already indicated, may draw a rectangle of the size of the printed plate and sketch within it the several figures in their respective sizes and positions. These "dummy" plates or layouts should be numbered as plates, and they may bear captions and titles. The photographs or drawings represented by the sketches should then be numbered to identify them with the sketches on the dummy plate, and those that pertain to each plate should be inclosed in an envelope attached to the dummy plate. A plate made up in this manner will meet every requirement of the photo-engraver or lithographer. If a paleontologist so desires, his plates can be permanently made up after he has transmitted his material, but he should always submit a tentative arrangement. REUSE OF ILLUSTRATIONS. If an author desires to use in modified form an illustration already published, whether by the Geological Survey or by an outside publisher, he should furnish a print or tracing of the illustration showing the changes desired. If the illustration is not to be modified he need only give the title of the volume in which it was used, with the number of the page, figure, or plate, and he need not make a sketch of the illustration or furnish a dummy; but its title should be quoted and proper reference should be given in the list of illustrations. Due credit should be given to the author or publisher. The original cuts of illustrations will be kept for one year after the report for which they were made has been published, and authors of later reports may and should reuse, whenever practicable, any such cut that will serve as an illustration. In the author's list of illustrations such a cut should be referred to by its number as plate or figure and the volume in which it was first used.