FIG. 1. Right abdominal lamina (× 2½) of a four-year-old juvenal male showing method of measuring growth-rings. The last growth-ring (4) was formed at the end of the 1954 growing season. The first growth-ring (H) marks the end of the season of hatching (1950). The umbilical scar (U) is faintly visible. The growth-zone for 1955 (specimen captured June 23) is just beginning to show in interlaminal seam. FIG. 2. _Left_--Right abdominal lamina (× 2) of subadult female, eight years old. The last growth-zone was formed in 1954. Note the relatively small growth increments in 1952 and 1953. The growth-zone for 1955 (date of capture, May 8) is not yet visible. This specimen grew more in the season of hatching (1946) than the specimen shown above in Fig. 1. _Right_--Interpectoral seam (× 3) of adult male showing slowness of growth in later life. The widest growth-zone seen here was formed in the tenth year and is followed by four zones too narrow to measure accurately. It is uncertain whether this specimen was still growing in the year it was captured (1923). [Illustration: PLATE 23] Ontogenetic change in color and markings of carapace. Radial markings begin to develop at the onset of epidermal growth. Markings are sharply defined in juveniles and young adults but may be obscured in later life by the encroachment of dark ground color or by wear on the shell. Figures are as follows: _Upper left_--Hatchling (× 1½); _Upper right_--Juvenile (× 1), one year old; _Lower left_--Juvenile (× 1), one year old; _Lower left_--Female (× 7/16) showing typical adult markings; _Lower right_--Adult male (× ½showing blotched pattern resulting from wear on shell. [Illustration: PLATE 24] Ontogenetic change in color and markings of plastron. Dark markings on plastra of hatchlings are unbroken. Dark radiations appear when epidermal growth begins. Figures are as follows: _Upper left_--Hatchling (× 1½); _Upper right_--Juvenile (× 1); _Lower left_--Female (× 7/16) showing typical adult markings; _Lower right_--Adult male (× ½) showing the effect of wear on markings. Plastra of old individuals are sometimes solid yellow. Note the break in the plastron that has healed and filled with ligamentous tissue. [Illustration: PLATE 25]