The illustrations and descriptive material in this publication will also be of considerable help in identification. Many illustrations of the more common invertebrate fossils have been included, but the publication was not designed primarily for use in fossil identification. Rather, it is intended to guide the amateur or student who is interested in fossil collecting, and to furnish suggestions as to how collecting may be more effectively pursued. USE OF IDENTIFICATION KEYS Fossil identification keys may be useful in helping the beginning collector identify specimens. The collector compares a fossil with the key description and eliminates those characters that do not fit the specimen. The key used in this handbook is based primarily on _symmetry_—the orderly arrangement of the parts of an object with reference to lines, planes, or points. The shape of the shell or body, presence or absence of coiling, and presence or absence of body partitions are also useful criteria in identifying fossils. To use the key the beginner should know something about symmetry. Two major types of symmetry are used in this key. 1. _Radial symmetry_—the symmetrical repetition of parts around an axis. This is the symmetry of a wheel, and any vertical section through the center of the object divides it into symmetrical halves (fig. 4a). 2. _Bilateral symmetry_—the symmetrical duplication of parts on each side of a plane (fig. 5). The plane divides the object into two halves that are mirror images of each other. This is the symmetry of a plank. It should be noted that many objects may have both kinds of symmetry. For example: A cone when viewed from the top has radial symmetry and when viewed from the side shows bilateral symmetry (fig. 4a, b). [Illustration: Fig. 4. Types of symmetry in a fossil coral. (a) Radial symmetry. (b) Bilateral symmetry.] [Illustration: Fig. 5. Bilateral symmetry as displayed by a typical fossil brachiopod.] An illustration of the use of the key on pages 26-27 follows. Assuming that a specimen displays radial symmetry, this means that it belongs under Part I on the key. If the fossil has a tapering, cylindrical, cone-shaped shell (“A” on the key), the subheadings under the “A” part of the key are examined. Should the specimen have a shell which is round, tapering at one end, with transverse septa or sutures (number 2 under “A”), it is probably a cephalopod. This is indicated on the right hand side of the page. Number 1 under “A” is eliminated because the fossil did not have longitudinal radial partitions within the shell.