Tapered shell Cephalopod b. Non-tapered, segments small and of relatively uniform thickness with hole in center; individual columnals disk-shaped Crinoid stem 2. Fossil composed of many-sided plates: a. Bud-shaped fossil of 13 wedge-shaped plates Blastoid b. Cup-shaped fossil of many curved plates surrounded by branching arms Crinoid II. Fossils displaying bilateral symmetry—symmetrical duplication of parts on each side of a plane A. Fossil coiled in a single plane: 1. Shell divided by internal transverse partitions or sutures Cephalopod 2. Shell without internal partitions or sutures Gastropod 3. Shell small; spindle-shaped; resembles wheat grain. Common in Pennsylvanian and Permian rocks Foraminifera (fusulinids) B. Fossil not coiled: 1. Shells or valves similar to clams: a. Plane of symmetry parallel to hinge; equivalved Pelecypod b. Plane of symmetry (almost bilaterally symmetrical) at right angles to hinge line; mostly inequivalved; strongly ribbed. “Scallop-like” with “ears.” Rare in Paleozoic rocks Pelecypod c. Plane of symmetry at right angles to hinge line; inequivalved; not “scallop-like” and without “ears.” Larger valve commonly has an opening in beak. Common in Paleozoic rocks Brachiopod 2. Fossil tapering, cylindrical, cone-shaped: a. Fossil with internal longitudinal, radial septa or partitions; cone-shaped Coral b. Shell with internal transverse partitions or sutures; tapering at one end Cephalopod c. Shell without internal septa or partitions. (1) Shell large, heavy; usually with external longitudinal ribs. Occur only in Cretaceous rocks Rudistid (2) Shell small (usually less than 2 inches), tusk-shaped, open at both ends. Rare in Paleozoic and Mesozoic rocks Scaphopod 3. Fossil heart-shaped, domed or flattened; radial star pattern on top