1933] Phases in the Development of Chrysemys Cinerea 53 



tween figrures 1 and 2. Hegner (1916) copies Gadow's figure. Dit- 

 mars (1914) says of C. marginata "size and structure of the shell, 

 like the preceding (i e., C. picta), differs only in coloration." If 

 color pattern were the only difference this form could well be grouped 

 as a variety of C. cinerea as will be shown later. However, in his 

 text descriptions Ditmars has overlooked the most characteristic dif- 

 ference shown in his drawings, (figs. 8 and 9) namely, that in C. 

 margmata the neural scutes alternate with the costal. This is not 

 true in C. picta. Since there was no opportunity to examine a large 

 number of specimens on this point, it is assumed that this arrange- 

 ment of the vertebral plates as indicated by Hermann (see figure 14) 

 is sufficient t9 separate C picta from the other species, and that C. 

 picta is best represented by this figure. 



Of the three remaining species Ruthven (1912) considers C. 

 marginata as synonymous with C. cinerea. He adopted the latter 

 specific name on the basis of priority, and thus describes but two 

 species, C. cinerea and C. bellii. These two species were separated 

 by certain carapace and plastron markings. Applying Ruthven 's 

 descriptions to the forms occurring at Madison, the separation of the 

 two species was impossible. Carapace markings were examined and 

 found to be variable and uncertain, in fact, carapace markings typical 

 of C. bellii occurred in animals having a typical C. cinerea plastron, 

 and vice versa. The conclusion that these carapace markings are 

 no longer of anj^ systematic value was confirmed by communications 

 from Ruthven. Differentiation, therefore, must be based wholly upon 

 plastron marking. Figs. 15 and 16 are copies of the plastron 

 drawings of these two species as shown by Ruthven. The former 

 represents C. bellii and the latter, C. cinerea. While there are indi- 

 viduals occurring here that have typical bellii plastrons, and others 

 which have typical cinerea plastrons, individuals have been found 

 with plastron markings intermediate between these two "species." 

 More than seven hundred turtles were examined, and practically 

 every degree of variation of plastron marking was found, ranging 

 from the typical C. oregoniensis, a common species upon the West 

 Coast, to a form with considerably less color pattern than that shown 

 by Ruthven for C. cinerea. Life size drawings were made (see figs. 

 17-24) of eight selected specimens showing some of these variations. 

 If plastron markings alone are to be the determining factor, where 



