[Illustration: FIG. 15. Lateral view of adult shell (× ¾), showing movable parts with anterior portion at left. (Abbreviations are as follows: ab, axillary buttress; hp, hypoplastron; hy, hyoplastron; ib, inguinal buttress; p5, fifth peripheral bone; th, transverse hinge).] [Illustration: FIG. 16. Medial view of adult shell (× ¾), showing movable parts with anterior portion at left. (Abbreviations as in fig. 15).] [Illustration: FIG. 17. Lateral view of adult shell (× ¾), showing scutellation of movable parts with anterior portion at left. (Abbreviations are as follows: ap, apical scale; ax, axillary scale; m5, fifth marginal scale; pl, pectoral lamina.)] The external scutellation of the plastral hinge in adults also differs from that in juveniles. In adults (Fig. 17 and Pl. 8) the transverse hinge is marked by ligamentous tissue between the pectoral and abdominal laminae; the forelobe of the plastron is distinctly narrower than the hind lobe. Two small scales lie near the corner of the hinge on each side. The larger and more anterior of these scales is the axillary; it is present in box turtles of all ages. The smaller scale (Fig. 17), to my knowledge, has never been named or mentioned in the literature; it is herein termed the apical scale. It is a constant feature in adults but is always lacking in hatchlings and small juveniles. Other scales, much smaller than the axillary and apical, occur on the ligamentous tissue of the hinge of some adults. [Illustration: FIG. 18. Plastron of hatchling (× 2), cleared and stained to show bony structure. (Abbreviations not listed in legend for Fig. 15 are as follows: af, anteromedian fontanelle; ep, epiplastron; pf, posteromedian fontanelle.)] [Illustration: FIG. 19. Carapace of hatchling (× 1½), cleared and stained to show bony structure; lateral view; anterior end at left. (Abbreviations as in Fig. 15.)] [Illustration: FIG. 20. Lateral view of hatchling (× 1); note the lateral process of the pectoral lamina (pl) extending posterior to the axillary scale (ax) in a position corresponding to the apical scale of adults. There is no external indication of the transverse hinge in young individuals. The yolk sac of this individual has been retracted but the umbilicus (umb) has not yet closed.] In juveniles (Fig. 20) the pectoroabdominal seam contains no ligamentous tissue and is like the other interlaminal seams of the plastron. A lateral apex of the pectoral lamina projects upward behind the axillary scale on each side, in the position occupied by the apical scale of adults. Examination of a large series of specimens revealed that the apical scale of adults becomes separated from the lateral apex of the pectoral lamina at approximately the time when the hinge becomes functional as such.