98 Kansas Academy of Science. 



paddle of Polycotylus latipinnis Cope, which is, I believe, re- 

 garded by Doctor Williston as a hind paddle. This seems to mean 

 that the above-mentioned characters are confined to the humerus, 

 which only serves to complicate our bewilderment. It has been 

 suggested that the pits, canals and cavities corresponded to simi- 

 lar structures in other vertebrate limb bones where the pits and 

 canals give passage to blood vessels, and the internal cavity cor- 

 responded with the medullary cavity. This may well be true, but 

 we still have to explain the presence of this peculiar groove which 

 is so highly developed on the present embryonic plesiosaurian 

 propodial. 



EXPLANATION OF FIGURES. 



Fig. 1. Dorsal view of the embryonic plesiosaurian propodial. The 

 groove will be seen on the right side of the figure. X 1. 



Fig. 2. Edge of the embryonic propodial, to show the shallow groove. 



XI. 



Fig. 3. Edge of the embryonic propodial, to show the deep groove. X |. 



Fig. 4. Edge of more mature propodial, showing an elongate groove 

 and three foramina. X |. 



Fig. 5. Opposite edge of distal end of propodial figured in 4. 



Fig. 6. Edge of a worn, nearly mature propodial of Polycotylus. X f . 



Fig. 7. Edge of a mature propodial of Polycotylus, showing the elon- 

 gate fissure at the distal end on one edge. X f . 



Fig. 8. Section through a mature propodial of an undescribed plesio- 

 saur. X J. 



Fig. 9. Lateral view of same propodial shown in figure 8. A = foramen 

 shown at A in figure 8. X \. 



Plate I. A series of plesiosaurian propodials, showing the evolution of 

 the shape of the bone. Two genera, Polycotylus and Elasmosaurus, are 

 possibly represented. Not all the bones figured show the pits, grooves and 

 canals. The small white nodule above the row at the right is a so-called 

 "epiphysis" belonging to an immature plesiosaurian propodial. The em- 

 bryonic bone described above is the last of the series to the right. X J. 



