540 BALANODON. 
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, 
(Balenide), 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 
