ABNORMALITIES IN CHELONIA. 



97 



sidered in the same category as the procaudals. On this account 

 I am strongly of the opinion that they have had a dermal origin 

 like the procaudals. 



4. Specimens 5, 6, 9, 13 and 49 have extra procaudal, either 

 single or double, and in each case this plate abnormality is asso- 

 ciated with the recurrence of an extra scute in the posterior part 

 of the neural row. The procaudals are certainly of dermal origin 

 and were probably the bony cores of the last neural scutes before 

 the crowding-out process began. Consequently the reappearance 

 of an extra plate and extra scute in this region may with justice 

 be considered as a case of correlation. 



5. Specimens 7, 8, 14, 17, 20, 21, 23, 27, 29, 31, 33, 41, 50, 

 51 and 58 have various kinds of scute abnormalities and per- 

 fectly normal plates. 



Summarizing, we find that the only invariable correlations are 

 in the marginals which represent scutes with their bony supports 

 (the plates) only slightly separated from one another ; that corre- 

 lations between extra procaudals (also true dermal plates) occur 

 in five cases and no case of plate abnormality in this region is 

 without a scute abnormality ; that correlations between an extra 

 neural of small size and irregular shape occur in every case ; that 

 extra paired costal plates are associated with asymmetrical extra 

 costal scutes ; and that very frequently scute abnormalities appear 

 without any corresponding plate abnormality. 



It would appear then that abnormalities are never truly corre- 

 lated except in regions where dermal plates persist and never in 

 the anterior part of the carapace, because the plates of that region, 

 except the nuchal, have given way to the periosteal plates of the 

 neural and costal series. The nuchal plate still possesses its 

 scute in a reduced condition, so we would not expect to find any 

 abnormality in that region. 



Only in the regions of dermal plates do we find any interde- 

 pendence of plates and scutes, because only here, according to 

 our theory, is there any genetic connection between dermal and 

 epidermal structures. 



That we find no true correlations between the plates and scutes 

 of the neural and costal series is just what we would expect from 

 our knowledge of their ontogenetic independence. In the most 

 irregular specimens, having the most grotesque scute displace- 



