ADAPTIVE MODIFICATIONS OF LIMB SKELETON 471 



shore to lay their eggs, and the Sirenia which have a peculiar 

 use of the paddle when feeding and holding the young, have 

 retained certain movable joints. 



Loss OF Tuberosities for Muscle Attachment. 



Naturally, upon the loss of movable joints or the need of 

 them, would follow the degeneration of the muscles of the limb 

 and consequently of the muscle attachments. This is plainly 

 evident in all the groups under discussion. The only tuberosi- 

 ties retained in the completely aquatic limb are those at the 

 head of the humerus and femur for the attachment of those 

 muscles which move the whole limb. 



In conclusion the writer wishes to thank the American Mu- 

 seum of Natural History for the use of material, and especially 

 to thank Professor Henry Fairfield Osborn for the use of his 

 library and for many valuable suggestions during the progress 

 of the work. 



Addendum. 



Since the above was written a very noteworthy paper by 

 Professor John C. Merriam has appeared in the Memoirs of the 

 California Academy of Sciences, May 5, 1905. In this paper 

 Professor Merriam describes the ** TJialattosaiiriay an entirely 

 new order of marine reptiles from the Triassic of California. 

 This group represents an offshoot of the primitive Diaptosauria 

 and is most nearly related to the Rhynchocephalia, standing in 

 relation to this group about as the Mosasaurs do to the Lacer- 

 tilia, according to Merriam. ' The two genera, Nectosminis and 

 Tkalattosaurus, in order of their specialization, exhibit no aquatic 

 characters not already mentioned, but in regard to the aquatic 

 adaptation of the limbs they fall in line in all respects with the 

 groups already discussed in the foregoing paper. Only the 

 propodial and epipodial elements are thus far known and these 

 seem to be about as much specialized as those of the later 

 Mosasaurs. The Thalattosauria are of interest in the present 

 paper chiefly because they add one more to the list of separate 



