210 



ORTHOGENETIC VARIATION IN THE SHELLS OF CHELONIA. 



£ 

 s 



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Size 



New born 

 New born 

 New born 



New born 

 4 inches 



New born 

 New born 

 New born 



New born 

 New born 



New born 

 New born 

 New born 

 New born 

 New born 

 New born 

 New born 



Locality 



B. M. Mazatlan 



Willey, 1 1 

 Willey, 12 



Willey, 13 

 Willey, 14 



Willey, 15 



Willey, 16 



Willey, 17 



Willey, 18 



Willey, 19 



Willey, 20 



B. M. Indian 



Seas. Theobald 



Coll. 



Willey, 7 

 Willey, 8 

 Willey, 9 



Willey, 10 



B. M. Philip- 6 



pines 



Observations 



Right 4th costal much reduced 

 Left 4th costal small 



Left 4th costal small, 

 right side. 



Only 12 marginals on the 



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 18 

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Left 4th costal small. Only 12 marginals on 

 either side ; the lateral corner is formed by the 

 4th. The first marginal is unusually long, 

 indicating previous fusion of two. 



5th neural very small. 



4th and 5th right costals small. 



This specimen seems to have only 6 neurals, but 

 in reality the 1st neural is composed of two 

 successive scutes as indicated by its size and 

 shape. Moreover the small size of the 4th 

 right costal scute indicates that the corre- 

 sponding neural (between the present 3rd and 

 4th has fallen out. The specimen can there- 

 fore be reconstructed into 8, 7, 7, and the last 

 but one neural (the present 5th) would be the 

 original 7th. This specimen bears great re- 

 semblance tn Xo. 17. 



4th left costal small. 



Right 4th costal small. 



Right 4th costal small. 13 right marginals, corner 

 formed by the 5th; 14 left marginals, corner 

 formed by the 6th. 



1st and 2nd neurals partly fused with each other. 



14 marginals on either side, the 1st marginal 

 scutes being very small. 



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13 left, 12 right marginals 



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