"ABNORMALITIES IN CHELONIA. 91 



unlikely to find vestigial scutes in this region unless a much 

 larger number of specimens is examined. 



Carapace abnormalities have been pictured by authors for over 

 a century and I have on my lists fourteen species, belonging to 

 widely diverse groups, that show the same general abnormalities. 



These scattering cases could scarcely be used in determining 

 the order of loss of scutes, but are of importance in that they 

 show that certain abnormalities that are comparatively rare in 

 Graptemys and CJiryseitiys occur with a fair degree of frequency 

 in other forms. For example: neurals 4 and 6, and costals i, 

 4 and 6 occur from 2 to 4 times in these specimens. The prev- 

 alence of abnormalities of this sort over such a wide range of 

 forms strengthens my idea of the universality of the process of 

 scute reduction in Chclonia. I have no doubt that such ab- 

 normalities will be found in any species if enough forms are 

 examined. 



In Gadow's diagrams illustrating the progressive reduction of 

 epidermal scutes (p. 217) it will be seen that the order of reduc- 

 tion differs from the one I have proposed in two points ; in the 

 first place he indicates that no. 10 neural is suppressed before 

 no. 8, but this is not borne out by his own figures. Figs. 4, 6, 

 7, 14, 20, 26, show no. 10 persisting after the total suppression 

 of no. 8, Fig. 26 being especially convincing. Figs. 8, 9, 10, 

 on the other hand, show no. 8 persisting after the suppression 

 of no. 10. The balance is decidedly in favor of the earlier sup- 

 pression of no. 8, yet there must have been some individual vari- 

 ation in this matter. My own figures show that no. 8 recurs 

 twelve times as compared with seventeen times for no. 10. In 

 my own specimens there are eight cases in which nos. 8 and 10 

 neurals recur together, nine cases of no. 10 recurring alone, 

 and only four of no. 8 recurring alone. It would seem then 

 that these two scutes were undergoing a process of suppression 

 at about the same time, but that no. 8 was in most cases the first 

 to disappear. 



In the second place it seems clear that no. I costal persisted 

 longer than no. 10 in Thalassochelys, but that the opposite was 

 the case in all the forms in my collection can scarcely be doubted, 

 no. 10 recurs thirty-six times and in many species, while no. i 

 recurs only six times. 



