1897.] QEINDIKG-TEETH OF THE MANATEE. 597' 



there are two more, 11"5 and 12*2 mm. long, which would be 

 nos. 5 and 6 of the full set (Plate XXXVI. fig. 1). 



Comparing this with the next-sized mandible (B.M. 1388/), 

 which shows the alveolus of one recently lost tooth, 4 teeth in place, 

 and 2 within the jaw, we cannot match the two posterior 

 teeth of the youngest jaw (nos. 5 and 6) with any teeth further 

 back in it than the 1st and 2nd of the standing teeth, respectively 

 10-7 and 11 "3 mm. long, while they may belong still further 

 forward, as there is a considerable difference in the ages of the two 

 specimens. However, even this matching makes the 7 teeth of 

 this second jaw to be numbers 4 to 10, the last having a length of 

 14-2 mm. (Plate XXXVI. fig. 2). 



The next jaw, 200 mm. long (B.M. 1388 d), gives evidence of 

 8 teeth, and comparing these with the last set we may match 

 no. 10 with the fourth, so that the posterior four would be 

 nos. 11 to 14; but it is by no means certain that the numbers 

 should not be even higher (Plate XXXVI. fig. 3). 



A similar comparison with another mandible 242 mm. long 

 (B.M, no. 94. 7. 25. 7) seems to show that the ten teeth of which 

 evidence is shown may be nos. 11 to 20 at the lowest, a result 

 that is fully supported by the other skulls available (Plate XXXVI. 

 fig. 4). Any error there may be in the enumeration is on the side 

 of making the total too low. 



No essential difference appears to exist between the dentition 

 of the upper and lower jaws, and we have therefore confined our 

 observations to the latter as being more convenient. It is true 

 that Dr. Kiikenthal assigns three premolars to the lower jaw and 

 none to the upper ; but all the skulls we have seen appear to have 

 a perfectly similar dentition above and below. 



Among the adult skulls both sexes seem to be represented, and 

 we have failed to find any possible cause of error in our calcu- 

 lations due to the factor of sex. 



We have therefore, by a method which appears to be perfectly 

 sound, arrived at a number identical with that which Lepsius con- 

 sidered would be the minimum outcome of Krauss's observations. 



But in trying to find out how many teeth a Manatee may have 

 in its life, a further complication is introduced by the remarkable 

 fact that in not a single specimen available to us, however large, 

 has the growth of additional teeth behind come to an end, so that 

 fresh teeth are apparently being produced to the close of the 

 animal's life. It would thus seem that a long-lived Manatee 

 might have a much larger number of teeth even than the 20 above 

 referred to, and, in fact, if any certain method of finding out the 

 exact number could be discovered, we should not be surprised if 

 the total were to amount to 30 or more. 



But even if there are only 15 or 18 teeth to be dealt with, we 

 are confronted with the very difficult problem of the origin and 

 homologies of these numerous teeth, and, after that, with the 

 bearing that their evolution has on that of other many-toothed 

 mammals. 



