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 vei"y great ; yet when the same elements in equivalent molars of the thick- and 

 thin-plated varieties of H. antiqims are compared we find more astounding differences. 



(1) Assuming A series to represent the second true molar of the smallest form, the 

 lengtli 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. Tlie 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 repi'esent 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, vol. vi. p. 296, Palisont. Memoirs, vol. ii. p. 202, pi. xi. figs. 1 & 1 a. 



