A MOUNTED SKELETON OF PLATECARPUS 539 



show this distal expansion of the tail, and which the author denies. He 

 also finds in the tail positive evidence of ninety-six caudal vertebrae 

 (including the pygals), and estimates, though I think on insufficient 

 foundation, twelve or fourteen more. (I may say, parenthetically, that 

 the position in which bones are found in the Kansas chalk has no value 

 as an indication of missing parts.) In the species T. proriger I have 

 found eighty-eight as the full number in a specimen, in which every 

 vertebra was found articulated, from the skull, to the minute ones of 

 the tail. This specimen I have recently re-examined in the University 

 of Kansas. There may have been one or two vestigial nodules at the 

 extreme tip missing. In this specimen there was no conjecture, each 

 vertebra as it was taken from its articulated position was numbered, 

 and placed in its original position in the mounted specimen. From 

 all of which facts it would seem to be evident that there may be 

 individual or specific differences as regards the number of vertebrae 

 in the mosasaurs. 



In comparison of the paddles as shown in this restoration and as 

 figured by Capps {op. cit.) it will be seen that the numbers of phalanges 

 do not quite agree. A further examination of the various paddles of 

 this genus leads me to the conclusion that the supposed missing 

 phalanges in the specimen figured by Capps were not real, and that 

 practically all the phalanges were secured. I think that the numbers 

 for the different toes were essentially those originally given by Marsh 

 for Platecarpus (Lestosaurus) . 



Here too, as is conclusively shown by a comparison of the paddles 

 of the American Museum specimen of Tylosaurus dyspelor with that 

 of Tylosaurus proriger of the University of Kansas, there are either 

 individual or specific differences. 



Huene finds in one of his specimens of T. dyspelor what he believes 

 to be vestigial nasal bones. I quite agree with him that the nasal bones 

 in the mosasaurs are not fused with the extremity of the premaxillae, 

 but I have never found in any of the numerous specimens of mosasaurs 

 any vestigial bones that seem beyond doubt to be the real nasals, 

 such as Huene figures. I have seen in several skulls remains of the 

 suture between the post-orbitals and post-frontals, but almost invari- 

 ably the suture is wholly obliterated, and it may be possible that the 

 nasal bones are thus indistinguishably fused in most specimens of 



