3i? The American Naturalist. [April, 
phosphate and carbonate of lime in genuine bones, whether 
we compare the different parts of the same bone, the different 
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bones of the same individual, or the bones of animals of differ- 
ent species. The same observation can be made for the pro- 
portion of fluoride of calcium which appears always to fall 
within the limit from 4 to } per cent. Chloride of calcium is 
almost always in less quantity than fluoride; it is the same 
with the oxide of iron except in the shell of the turtle trionyx 
(IX). It is necessary, nevertheless, to notice some exception 
in this constancy of proportion in bony substances of special 
nature, like the teeth or tusk of the elephant and the shell 
of the turtle. The phosphate of magnesia, almost always less 
than 2 per cent, is raised to near 4 per cent in the tooth of the 
elephant (VI) and passes 15 per cent in the tusk of the ele- 
phant (VII) of which it contributes, possibly, to augment the 
compactness and resistance. At the same time the carbonate 
of lime which often forms more than 9 per cent of the sub- 
stance of bone, drops to 2 per cent in the ivory. The carbonate 
of lime is sensibly in superior proportion in the average of bones 
of herbivorous animals, and above all, in those that live in 
water, the manatee and the turtle (IV, IX, X). 
The principal object of this paper has been to compare mod- 
ern bones with fossil bones of similar species in order to dis- 
cover the relative amount of fluorine and phosphoric acid, and 
to that end numerous analyses have been made, the results of 
which can better be given in the form of a table. 
