VOL. LXXIV.J 



PHILOSOPHICAL TRANSACTIONS. 



543 



if we allow that before the accident the animal was in possession of perfect teeth, 

 it follows also, that they were consumed and replaced by imperfect ones. There 

 were 6 teeth in each row, and 52 rows, making together about 312 teeth. Now 

 allowing the consumption to have been equal in all parts of the jaws, it follows, 

 that the animal had already consumed 312 teeth, and was in possession of a like 

 number for future consumption. The teeth of sharks, rays, &c. may be divided 

 into active and passive. The active teeth are the anterior ones of each row, 

 standing with their points upwards. The passive teeth are the remaining ones, 

 lying one over another, like the tiles on a house (imbricated,) with their points 

 downwards. It appears from the foregoing account, that the anterior or active 

 teeth had been replaced 6 times ; and that they might have been renewed 6 times 

 more, making in all 12 times. From which it may be reasonably concluded, 

 that this does not happen any precise number of times ; but that the renovation 

 is perpetual during the life of the animal. 



XXL Abstract of a Register of the Barometer, Thermometer, and Rain, at 

 Lyndon, in Rutland, 1783. By Thomas Barker, Esq. p. 283. 



