II In organizing Dr. Cheever's collection it was decided that the slides be divided into four groups, sections A, B, C and D. Into Section A were placed all those slides which bore determinations. Into Section B was placed all those slides which were undetermined, but which bore collection localities. Also included in Section B was a number of slides, which turned up after the major reorganization had taken place and which are treated in the agenda. Section C was catch all for those slides which were not ident- ified and which bore no collection localities. Section D was set up to contain the following three diatom exsiccati: Diatomacearum species typicae (no. 1-700); Cleve and Moller's Diatoms (no. 1-300); and Synopsis Des Diatomees de Belgique (no. 1-550). Section A Boxes A-1 to A-41 Determined slides are indexed alphabetically according to genus and then according to species. The actual location of the slides are given by letter number combinations located on the extreme right handside of the page following each species entry. For example the letter number combination of Alloineis antillarum is A-3: 24. The letter number sequence A-3 indicates box 3 of Section A. The number "24" following the colon in that sequence indicates the slot number. During the organization of the collection, all slides which listed more than one species were without exception inserted in the collection under the first name listed on the slide. All the species were then listed in the index giving the same letter-number combination. Thus a given slide may be found listed under more than one diatom species and likewise the letter-number combinations given after a species may on occasion appear to be out of sequence. Section B Boxes B-1 to B-41 A-llundetermined slides bearing collection localities are divided into two groups. Those collections made in the United States are in Group I and are arranged alphabetically by state. Those collections made outside the US are in the Group II World division. The slides in the Group II are divided into geographic areas and arranged alphabetically by country or locality within each area. The locations of the slides in Section B are as Section A given in the index by the letter-number combinations following each entry. Section C Boxes C-1 to C-5 The slides in this section are probably of culturing experiments. They are undetermined and bear no collection data; they are therefore not indexed. Section D Boxes D-1 to D-18 Diatomacearum species typicae D-1 to D-7 Cleve and Moller's Diatoms D-8 to D-10 Cleve and Moller's Diatoms Incomplete set D-11 to D-12 Synopsis Des Diatomees de Belgique D-13 to D-18