28 MR. A. L. ADAMS ON THE OSTEOLOGY OF 
are alike. But the difference in the thickness of the plates and their enamel is cer- 
tainly very great; yet when the same elements in equivalent molars of the thick- and 
thin-plated varieties of Z. antiquus are compared we find more astounding differences. 
(1) Assuming A series to represent the second true molar of the smallest form, the 
length of the first molar would be to the second as 4:2 to 5°6 inches. 
(2) Allowing B series to belong to a variety of thin-plated molars of the largest form, 
and C series a larger thick-plated sort, their lengths, as compared with the first true 
molar, would stand as 6°5 and 7 inches to 4:2 and 5 inches. Now, as individual differ- 
ences in the size of first and second true molars in all other known species vary very 
much, there is nothing in these discrepancies very discordant as compared with them. 
In the African Elephant the first true molar often varies in the upper jaw as much as 
an inch in individual molars holding the same number of ridges; and the like is the 
case to a greater extent in the Asiatic, whilst teeth referable to the second true molar of 
the Mammoth, and holding eighteen ridges, I have found to vary as much as 2 inches. 
7. The Third or Last True Molar. 
The last of the dental series is well represented in my collection by several entire 
specimens, which therefore fix in certain instances the dimensions, ridge-formula, and 
characters of this important molar beyond reasonable doubt. At the same time there 
are conflicting data in regard to the characters of specimens; and, as in the penulti- 
mate milk-molar, they form a series graduating from what is evidently a very small last 
molar up to a large one; and this progression is so gradual that I find it difficult to 
separate the intermediate from either of the extremes, which, however, differ widely in 
characters as well as dimensions. Although certain types held 14 to 15 ridges, or 12 
to 13 plates and 2 talons, it is not evident that all I have considered last true molars 
contained so large a ridge-formula. 
A Series (thin-plated).—1. In the first place I will select as a type of this series the 
finely preserved molar considered by Falconer to represent the last upper molar of the 
Elephas melitensis’. This tooth I have carefully compared with similar specimens in 
my own collection, more especially No 28 from Mnaidra Gap, with which it agrees very 
closely; indeed so similar are they in general characters that, were it not that both belong 
to the right side, it would at first sight be difficult to discriminate the differences, which, 
however, are important. No. 28 has an additional ridge; and a portion of its posterior 
talon has been recently broken off. In front there is a field of dentine, where doubtless 
another ridge or ridges existed; and whilst ten ridges are contained in 4 inches in the 
Zebbug specimen, there are eleven in 4°4 inches in No, 28. Dr. Falconer has pointed 
out that in the former the large front fang and its ridges have disappeared by ab- 
sorption and attrition; and as this root usually upholds three ridges, it is fair to surmise 
that the Zebbug molar may have originally been about 5 inches in length, perhaps a 
‘ Zool. Trans, yol. vi. p. 296, Palaont. Memoirs, vol. ii. p. 292, pl. xi. figs. 1 & la, 
