Vol. X. February, 1906. A r o. 



BIOLOGICAL BULLETIN 



THE SIGNIFICANCE OF SCUTE AND PLATE 

 "ABNORMALITIES" IN CHELONIA. 



A CONTRIBUTION TO THE EVOLUTIONARY HISTORY OF THE 

 CHELONIAN CARAPACE AND PLASTRON. 



H. H. NEWMAN. 

 CONTENTS. 



PART II. 



PAGE. 

 IV. The "Tail-trunk" of Chelydra serpentina, as a Close Approximation to 



Ancestral Conditions of Carapace and Plastron 99 



V. Further Evidence of the Former Existence of a Dermal Carapace in Che- 

 Ionia, as Derived from Specimens of Graptemys... 103 



VI. The Color Pattern of Chelonia as Confirmatory Evidence of the Former 



Existence of Dermal Armor 106 



PART II. 



IV. THE TAIL-TRUNK OF CHELYDRA SERPENTINA AS A CLOSE 

 APPROXIMATION TO ANCESTRAL CONDITIONS OF CARA- 

 PACE AND PLASTRON. 



Baur, Hay and others have used as the hypothetical ances- 

 tral form an aberrant and perhaps highly specialized Chelonian, 

 DcrmacJielys coriacea, but in the light of the various atavistic re- 

 currences discussed in this paper and in view of the fact that 

 certain definite rows of scutes invariably predominate over others, 

 I have been led to seek elsewhere for primitive conditions. 



A closer approximation to the true ancestral conditions is, I 

 believe, to be seen in that portion of the trunk of Chelydra that 

 is commonly called the base of the tail. Here if anywhere one 

 would expect to find primitive conditions. The Chelydridae are 

 generally acknowledged to be our most generalized chelonians, 



99 



