G. It. Wieland—On Marine Turtles. 339 



and not markedly modified for marine life, so that Toxochelys 

 " did not navigate the open seas." 



In support of his contentions Dr. Hay uses a percentual 

 method of comparison in which the humerus is conveniently 

 and arbitrarily considered the unit in terms of which the 

 length of the digits is expressed. This very effective means 

 of comparison was first used by the writer in the case of forms 

 in other ways related, and is, within limits, unquestionably 

 useful in a diagrammatic sense. But Dr. Hay now mistakenly 

 employs it in a far wider application than originally contem- 

 plated, when he reaches direct conclusions as to the front limb 

 of Toxochelys by comparison with the Trionychid Amycla 

 spin if era, thus : — 



Arm. 









Fingers. 





Humerus. Eadius. 

 Amy da 100 53 

 Toxochelys 100 58 



Ulna. 

 51 

 50 



1st. 

 69 

 51 



2d. 

 90 

 73 



3d. 4th. 



98 116 



100+ 104 + 



5th. 



98 



70 + 



One might as well go on to prove that the " hawks-bill," 

 Erebmochelys imbricata, is unable to " navigate the open seas". 

 — For similarly : 



Arm. Fingers. 



Humerus. Eadius. Ulna. 



1st. 



2d. 



3d. 4th. 



5th. 



Amycla 100 53 51 

 Eretmochelys 100 53 44 



69 

 49 



90 



89 



98 116 

 128 105 



98 

 44 



Whence the following differences : 











Arm. 







Fingers. 





Humerus. Radius. Ulna. 



1st. 



2d. 



3d. 4th. 



5th. 



Amy da _ _ _ . + 7 

 Eretmochelys 



+ 20 



+ 1 



._ +11 

 + 30 .. 



+ 54 



It is clear that save for that short thumb and long fourth 

 finger of Eretmochelys, w T ere this an extinct form, no conclu- 

 sive evidence of the true nipper development would be afforded 

 by snch measurements as the above when considered alone. 

 For it is a noteworthy fact that the disparity between the 

 thumb and fourth finger of Amy da is + 47 as against +53 in 

 Toxochelys, and +56 in Eretmochelys. Yet as a true indi- 

 cation of unequal finger development, instead of disparity 

 between only the short first and the long third and fourth 

 fingers, as in Eretmochelys, there was in Toxochelys strong dis- 

 parity between the short first and second and the long third 

 and fourth fingers. There was also ulnar disparity. 



All these fundamental numerical relations have been over- 

 looked in Dr. Hay's criticism. He entirely ignores, too, the 



