210 Geological Society. 



Jan. 9, 1839. — X paper was read, entitled, " Observations on the 

 Teeth of the Zeaglodon, Basilosaurus of Dr. Harlan," by Richard 

 Owen, Esq., F.G.S. 



During the recent discussions respecting the Stonesfield fossil 

 jaws, one of the strongest arguments adduced and reiterated by 

 M. de Blainville and others in support of their saurian nature, was 

 founded on the presumed existence in America of a fossil reptile 

 possessing teeth with double fangs, and called by Dr. Harlan the 

 Basilosaurus. To the validity of this argument, Mr. Owen refused 

 to assent, until the teeth of the American fossil had been subjected 

 to a re- examination with an especial view to their alleged mode of 

 implantation in the jaw ; and until they had been submitted to the 

 test of the microscopic investigation of their intimate structure 

 with reference to the true affinities of the animal to which they be- 

 longed. The recent arrival of Dr. Harlan in England with the fossils, 

 and the permission which he has liberally granted Mr. Owen of 

 having the necessary sections made, have enabled him to determine 

 the mammiferous nature of the fossil. 



Among the parts of the Basilosaurus brought to England by Dr. 

 Harlan, are two portions of bone belonging to the upper jaw ; the 

 larger of them contains three teeth ; the other, the sockets of two teeth. 

 In the larger specimen, the crowns of the teeth are more or less perfect, 

 and they are compressed and conical, but with an obtuse apex. The 

 longitudinal diameter of the middle, and most perfect one, is three 

 inches, the transverse diameter one inch two lines, and the height 

 above the alveolar process two inches and a half. The crown is trans- 

 versely contracted in the middle, giving its horizontal section an 

 hour-glass form ; and the opposite wide longitudinal grooves which 

 produce this shape, becoming deeper as the crown approaches the 

 socket, at length meet and divide the root of the tooth into two se- 

 parate fangs. The two teeth in the fore part of the jaw are smaller 

 than the hinder tooth, and the anterior one appears to be of a sim- 

 pler structure. 



A worn-down tooth contained in another portion of jaw, Mr. Owen 

 had sliced, and it presented the same hour-glass form, the crown 

 being divided into two irregular, rounded lobes joined by a narrow 

 isthmus or neck. The anterior lobe is placed obliquely, but the 

 posterior parallel with the axis of the jaw. The isthmus increases 

 in length as the tooth descends in the socket until the isthmus finally 

 disappears, and the two portions of the tooth take on the character 

 of separate fangs. 



The sockets in the anterior fragment of the upper jaw are indistinct 



