11. The Short hinge line helps distinguish the pentamerids from the ancestral orthids from which they are obviously derived. 12. The fin and rudder formed a tilted, cropped parallelogram with a hinge line above that of the elevator. 13. With progressive subsidence of the basin during the Pennsylvanian, the western basin hinge line and carbonate shelf, continued migrating west. 14. These flaps are slotted and are each in two spanwise parts, the break placed at the wing fold hinge line . 15. The beak is slightly elevated above the hinge lines and the beak sculpture consists of 3 to 5 wavy lines. 16. The glacier has a hinge line , the point at which its projecting tongue leaves the sea bed and starts to float. 17. All ark shells have a long straight hinge line with a single row of numerous small and unspecialized " teeth ". 18. The hinge line corresponds to the animal's dorsal side, though when living it usually rests " sideways ", on its right. 19. The two valves usually articulate with one another using structures known as " teeth " which are situated along the hinge line . 20. The outer portions were more lightly constructed, and designed to snap off at the hinge line if the g-force exceeded 7.5 g.
