2 Robert E. Coker. 



PAGE 



Neurals G3 



Adjustment of JMeurals aud Costals G4 



"Incomplete Division" 65 



Part III. Significance of the Abnormalities G7 



Introduction G7 



External Conditions G8 



Inheritance G9 



Atavism 69 



Summary of Part III 73 



Note 73 



Literature cited 74 



Explanation of Plates 75 



Introduction. 



At the begiuning of an inquiry regarding the diamond-back ter- 

 rapin, Malaclemmys centrata (Latr.), undertaken in 1902, raj atten- 

 tion was attracted bj the frequent instances of striking deviation 

 from the ''normal" number and arrangement of the horny scutes 

 of the carapace. The anomalies seemed of sufficient interest to justify 

 a record of the facts, and accordingly were included in the notes 

 made in connection with the economic study then in progress. Later, 

 the study was extended in some lines, as it was seen that the anom- 

 alies might have some significance for theoretical interpretation or 

 experimental study. 



For kind permission to use in this paper such data as was obtained 

 while employed in the economic study of the terrapin, my acknowl- 

 edgmient is due to Hon. George M. Bowers, United States Commis- 

 sioner of Fish and Fisheries, and to Professor J. A. Holmes, State 

 Geologist of North Carolina. My thanks are also due to the officials 

 of the Bureau of Fisheries and to Dr. Caswell Grave, Director of 

 the Fisheries Laboratory, for many courtesies extended to me while 

 occupying a research table in the Laboratory. 



I wish to make grateful acknowledgment of my indebtedness to 

 Prof. W. K. Brooks, under whose guidance the study has been prose- 

 cuted. 



Character of the Diversity. 



At first I was particularly impressed by the comparatively great 

 prevalence of apparent "abnormalities" in the number of horny 



