540 BAL^ENODON. 



the axis of the dentine at its base is nine lines ; that 

 of the coat of cement is from six to seven lines. The 

 dentine is continued to the apex, forming the obtuse end 

 of the crown, as in the worn teeth of the Cachalot. 



The smaller dental fossil transmitted by Professor Hens- 

 low, is part of a longer and more tapering cone than the 

 larger one, and thus recedes further from the Cachalot's 

 form of tooth ; but the dentine is thicker in proportion to 

 the cement than in the foregoing fossils, and in so far the 

 present resembles more the Cachalot's tooth in structure : 

 where the cone has a diameter of one inch, for example, 

 the dentinal axis, is seven lines across, and the cement 

 three lines in thickness. The exposed surface of the den- 

 tine shows the small, close-set, slightly wavy, longitu- 

 dinal grooves; and the microscopic structure of both 

 fragments agrees with that of the first-described specimen. 



The mere difference of form in the fossil teeth might 

 depend, according to the analogy of the Physeter, on a 

 difference of age in the individual, or of place in the 

 jaw, from which such fossils have been derived ; but the 

 different relative proportions of dentine and cement in 

 the slender conical tooth, indicates a distinction of species. 



We have seen that four species of Cetacea, referrible 

 by the form of the tympanic bones to the Whale family, 

 (Baltenida), but distinct from all known existing species 

 of that family, are more definitely indicated by the re- 

 markable fossils, termed Cetotolites ; and it is not im- 

 probable that these and the teeth may have been parts 

 of the same Cetaceous animals. We know that the great 

 Whale-bone Whales of the present day, before their 

 jaws acquire the peculiar array of baleen-plates, mani- 

 fest a true dental system, although the fetal teeth are 

 transitory and never destined to cut the gum. And as 



