24G ON THE EXTINCT MAMMALIA OF 



in form, size, and mutilation. The two certainly resemble each other so much that 

 one would do as well as the other to represent the species. 



The tooth of enigmatic character, above referred to, preserved in the Museum of 

 the Academy, to which the cast just described bears a resemblance, was purchased in 

 London, as an American fossil, through Mr. Edward Charlesworth, and sent to Dr. 

 T. B. Wilson, by whom it was presented to this Institution. By a wonderful coinci- 

 dence of circumstances, it was mistaken for the original of the cast above described, 

 and was without dissent believed to be such until the discovery of the cast in Dr. 

 Harlan's collection proved it to be otherwise. In comparing the specimen with the 

 cast above described, it is observed that the two teeth nearly resembled each other in 

 general construction, proportions, size, accidental color and fracture, and position in 

 the series. When we add to these characters of resemblance that both specimens 

 were of reputed American origin, were different from the corresponding teeth of the 

 M. americamis, and were the only ones of the kind discovered, it is not to be wondered 

 that the tooth under consideration was unhesitatingly admitted to be the original of 

 the cast. It is the tooth figured by Dr. Warren in his work on the Mastodon glgan- 

 teus, marked Mastodon angustidens ?, and is referred to on page 79 under the head of 

 " the Baltimore tooth." Dr. Warren remarks that while examining the Mastodon 

 teeth in the collection of the Academy of Natural Sciences, "Dr. Hays, fixing on one, 

 immediately said : ' This is the Baltimore tooth we were looking for, or it is so like 

 it as not to be distinguished from it.' " It was also to this specimen that the extract 

 from Mr. Charlesworth's letter refers, in Appendix C, page 176, of the same work. 

 Mr. Charlesworth wrote : " Some time in 1847 or 8 I was passing through an obscure 

 alley connecting Lincoln's Inn Fields with Temple Bar, when my attention was 

 arrested by a Mastodon tooth in a shop window, which seemed to me a fac-simile of 

 the one I had examined with so much interest in the Baltimore Museum. The pro- 

 prietor of the shop told me he had bought the tooth as American at one of Steven's 

 sales, the well-known natural history auctioneer at Covent Garden. We struck a 

 bargain for the fossil, and I shortly afterwards sent it to Dr. Wilson, with a state- 

 ment of its remarkable resemblance to the tooth which I supposed still to be safe in 

 the Baltimore Museum." 



The tooth, represented in figure 14, plate XXVII, is a last lower molar of the left 

 side, rather smaller than the plaster cast, but presenting about the same proportions 

 of breadth fore and aft to the width. 



The crown exhibits four principal divisions or ridges, together with a heel consist- 

 ing of a rudimental fifth division, separated by four transverse valleys. The middle 

 of the latter is occupied by accessory eminences, and a thick basal ridge completed 

 the fore part of the crown. 



The four principal divisions of the crown are of nearly uniform development, and 



