80 KANSAS UNIVERSITY SCIENCE BULLETIN. 



site. At this rate, each bit of alveolar border would function 

 three times during the life of the fish. It may be urged thac 

 the dentary is growing all this time and that the increasing 

 size of the interspaces would prevent any complications. Each 

 successive set of teeth is larger than its predecessor, and 

 obviously the ratio of the diameter of the teeth to the length 

 of the dentary would remain a constant throughout the life of 

 the fish. Instead of the growth of the dentary making the 

 problem more simple, it only prevents it from being more 

 complex than it has been stated. 



It can easily be seen that each new palatine fang has a dis- 

 tinct base, and no tooth ever appears on any of the old cres- 

 centic scars left by previous fangs. Also, in case of the dent- 

 ary fang, there is never a tooth on any of the scars of fangs 

 which have been shed. Careful examination of all of the 

 specimens of palatines and symphysial portions of dentaries 

 fails to reveal any sign of development of a new fang on a 

 site where there had been a fang standing before. The cres- 

 centic scars of the shed palatine fangs extend from the base 

 of the fang to the caudal end of the osteodentine of the pala- 

 tine, and the scars left by the dentary fang extend from the 

 base of this fang nearly to the cephalic end of the dentary. 

 These portions are always found to be edentulous. 



This would suggest a negative answer to the question. 

 There are several specimens of dentaries and pterygoids which 

 may be of some assistance in explaining the nature of this 

 process. A dentary of specimen No. 803 (pi. Ill, fig. 9, den), 

 which shows an especially typical alveolar border, has been 

 refigured in plate II, figure 2, showing the mesial aspect. Un- 

 like the palatine, the tooth scars of the dentary show only on 

 the mesial side. The contour line, /-/, shows the relative de- 

 gree of absorption of the bases of the teeth. The bases of 

 teeth most recently discarded, viz., those immediately caudad 

 to b, c, d, and c, are least absorbed ; while the older bases, im- 

 mediately cephalad to b, c, d, and e, are most absorbed, but 

 the osteodentine never entirely disappears from the alveolar 

 surface. The latter scars are as large as those just caudad to 

 b, c, d, and e; hence they must have been bases of full-sized 

 teeth. Since replacement of the palatine fang commences 

 when the fish is quite small, as shown by the crescentic scars 

 on the ventral surface of this bone, it is reasonable to suppose 



