96 Kansas Academy of Science. 



described above. Its bottom is rough and has the openings of at 

 least three distinct foramina, with many smaller vascular openings. 



It has been observed that the structure of the immature plesio- 

 saurian propodial is more dense than is the case in fully matured 

 bones. This holds true for the present specimen. The density of 

 the embryonic propodial is undoubtedly due to the fact that the 

 bone cells have not yet become vascularized. This dense condition 

 of the perichondrium is not confined to the bones of plesiosaurs, 

 since the same characters are found in the limb bones of young 

 alligators and lizards. 



The presence of the grooves and foramina appears Ifo be peculiar 

 to the plesiosaurian propodial. The writer has examined, during 

 the past few months, the embryonic skeletal systems of numerous 

 specimens of several sjpecies of turtles, lizards and the American 

 alligator. In none of these has he been able to distinguish any 

 structure which could be correlated with the grooves and foramina 

 found in the plesiosaurian propodial, but it has been observed that 

 the structure of the perichondrium is more dense in the embryonic 

 limb bones than in the bones of the adults of the same species. 

 The exterior surfaces are smooth. Possibly the degrees cf density 

 of the limb bones of vertebrates is to be correlated with the rate of 

 growth of the animal. It is a matter of easy observation that dif- 

 ferent immature plesiosaurian propodials offer different degrees of 

 density of structure even among the embryonic bones. The above- 

 mentioned foramina and grooves have not been described, so far as 

 I am aware, in the limb bones of any adult vertebrate, recent or 

 extinct. 



The present example of plesiosaurian propodial measures 83 mm. 

 in length by 31 mm. in width. It tapers somewhat at each end, 

 with the greater width at the distal end. There is a distinct rough- 

 ening of the surface in several places, near the edges, which do not 

 have the same characters as the muscular roughenings of the adults, 

 but seem to be due to blood vessels in the caps of cartilage which 

 undoubtedly covered the ends and sides of the bone. 



The deep groove, present on one edge of the bone, is peculiar 

 both in its extent and width. It has hitherto not been observed 

 on immature plesiosaurian limb bones. It fills nearly the entire 

 radial (?) edge. Its edges are sharply defined and its bottom is 

 marked by numerous small and a few large vascular pits, giving the 

 surface a punctate appearance. Somewhat more than half beyond 

 the length of the bone distally there is a large, rough tuberosity, prob- 

 ably due to some disease or accident, as it is very vascular, like most 



