Geological Papers. 97 



exostosial growths. It recalls, for instance, the pathological growth 

 known as the "lump- jaw" of cattle, which is familiar to travelers 

 on the western plains. This pathological interruption occupies 

 15 mm. of the bottom of the groove. It lies just over the opening 

 of a rather large canal, which gives passage to a calcite-filled cavity 

 in the center of the bone. This cavity is paralleled by the condi- 

 tion found in the more mature propodial shown in figures 8 and 9. 



Grooves of a similar nature have been observed on more mature 

 material. There are examples of several adult and immature pro- 

 podials in the collection which show these grooves, and a few of 

 them show the foramina as well, as is shown in figures 4, 5, 6, and 

 7. Three foramina are shown in figure 4 and one in figure 9, In 

 the adult and less mature propodials the grooves never extend the 

 entire length of the bone, but are restricted to the distal one-third, 

 or, at most, to the distal half. In five specimens there are grooves 

 present on both edges of the bone, as shown in one instance in fig. 

 ures 4 and 5. 



The pits and foramina opening into the canals which pass to 

 the internal cavities usually occur on the edge opposite the groove, 

 but occasionally they occur on the same edge, and in case the 

 groove is present on bot^i edges the foramina are present at times 

 on both edges also. The specimen outlined in figure 4 has the 

 grooves on both edges. On the edge represented in figure 5 there 

 is a single foramen, while on the edge shown in figure 4 there oc- 

 cur three foramina. The specimen outlined in figure 6 shows no 

 pits at all, and the groove occurs only on the edge where it is fig- 

 ured. The adult bone of figure 7 has no pits and the groove is 

 confined to one edge. 



The meaning of these various grooves, foramina, pits, etc., is 

 rather difficult to perceive. Judging from the condition found in 

 the embryonic bone described above, one might be correct in say. 

 ing that there were two ossific centers for the perichondral bone. 

 But there are immature propodials and mature ones which show 

 not the slightest signs of the pits, grooves or foramina, nor, on sec- 

 tioning, does any evidence of the internal cavity appear. So far 

 as I am aware, all propodials which exhibit these structures belong 

 in the genus Polycotylus. I do not recall that they have ever 

 been detected in bones assigned to Elasmosaurus, Trinacromerum 

 or Plesiosaurus. Certainly there are no evidences of them in the 

 propodials of these genera which are accessible. And, oddly 

 enough, they do not occur in all examples of Polycotylus, for they 

 are not found in the propodial associated with a nearly complete 

 -7 



