348 



CHELONIA 



CHAP. 



painted across. The nuchal shield is elongated and very narrow, 

 its. anterior edge and that of the neighbouring marginals are finely 

 serrated. Very young individuals are at once recognised by the 

 prominent longitudinal median stripe of bright orange extending 

 over the nuchal and neural shields ; the yellow transverse bands 

 are still absent ; they appear when the longitudinal line vanishes. 

 The " Painted Terrapin " is one of the few species of which, 

 thanks to L. Agassiz, 1 complete data of growth from the new 



FIG. 76. Chrysemys picta, "Painted Terrapin." x |. 



born to old age are known. During the first six or seven years 

 the rate of growth is so uniform that numerous specimens 

 collected at the same time are readily arranged in sets of the 

 same age, simply by the differences they show in their size. The 

 successive lines of growth on the shields indicate the number of 

 years. After the seventh year the age is much more difficult to 

 distinguish in those tortoises, which, like Ch. picta, have a 

 perfectly smooth epidermis. This smoothness is due to the fact 

 that the shields undergo a process of moulting. An upper, quite 

 1 Contributions to the Nat. Hist, of the U.S.A., Boston, 1857. 



