266 Proceedings of the Royal Physical Society. 



crowns much worn down and hollowed out in the middle, 

 showing the central brown dentine, surrounded with a 

 coat of enamel, and a slight outer layer of dark coloured 

 cementum. 



There are fifteen molar teeth remaining in the upper jaw, 

 and fifteen in the lower, with six distinct empty sockets ; 

 the dental formula in the skull from Honduras is, therefore, 



9 — 9 



m g — g =36. It appears to have been from the American 



species, the Mandtus australis of the British Museum Cata- 

 logue, that Daubenton, Cuvier, Gray, and others, have 

 adopted the dental formula of the genus Manatus. In the 

 British Museum Catalogue for 1850, the number of grinders 

 in the genus Manatus is said to vary according to the age or 



9 — 9 



state of the specimens, but when complete to be m ^ — ^ = 36. 

 It is added that the front ones are often deciduous ; hence 



^» g 



Sir Everard Home describes them as m ~ — - n = 24, and 

 8-8 



Cuvier as m g— g = 32. 



There is no skull of the African species mentioned in the 

 Catalogue as existing in the British Museum ; and there is 

 none described in the Catalogue of the Eoyal College of Sur- 

 geons of London ; and at a meeting of the British Associa- 

 tion held at Cheltenham in 1856, Professor Owen stated, 

 that he had not then had an opportunity of examining the 

 dentition of the known African Manatee. 



The difference in the number of the molar teeth in these 

 two distinct species corresponds with the difference in the 

 length of the aveolar portion of the palate, and with other 

 corresponding modifications which have been shown to 

 exist between the two skulls. 



I am indebted to Professor H. D. Eogers of Glasgow for 

 an opportunity of comparing the skull of the Mandtus aus- 

 tralis, with that of the Mandtus senegdlensis ; and the result 

 of this anatomical comparison appears to me to justify the 



conclusion, that m ^ — ^ — 44, is the normal number of 



the dental formula for the genus Manatus, as this number 



