6 DR. R. W. GIBBES ON THE 



This fossil was found at Leognan, a few leagues south of Bordeaux, in the calcaire 

 grossier, or Eocene. The form of the fragment he describes thus : 



" Le museau est alonge, deprime et va en s'amincissant comme dans le rostre des 

 crocodiles et de certains lezards. Sa longueur est d'environ dix-huit pouces, et n'est 

 pas meme complete. * * * Ce qui rend cet os fossile fort precieux, c'est la presence de 

 quatre dents posterieures, implantees dansleurs alveoles. Le sommetdes trois est un 

 peu endommage, mais la plus grande est d'une integrite admirable. Elles sont fortes, 

 epaisses, subtriangulaires, pointues, comprimees, et aplaties lateralement, un peu 

 arquees en dedans, forte ment dentees en scie, ou plutot crenelees en leurs bords; 

 celui-ci est tranchant. Les dentelures sont profondes, inegales, plus multipliees du 

 cote de la tete de I'animal. II y en a cinq sur ce bord, a la dent integre, 

 et deux seulement au bord oppose. Les dentelures presentent, a leur tour, de 

 fines denticulations. En resume, la forme de ces dents rappellent celles des dents 

 de squale ; et les details des dentelures, rappellent faiblement aussi, ceux de la 

 structure des dents de I'iguanodon. La hauteur de la dent bien conservee est de 

 seize lignes, hors de I'alveole, d'un pouce. Le diametre, sur ce point, est de six 

 lignes, tandis que vers la pointe il n'a que deux lignes et demie. La racine est de 

 forme conique ; sa longueur doit egaler celui de la profondeur de la cavite alveolaire, 

 qui est de neuf a dix lignes, comme je viens de I'indiquer." (PI. L, fig. 5.) 



He doubted whether to refer it to Cetacea or Sauna]; and finally came to the con- 

 clusion that it constituted a new order of amphibious reptile — a carnivorous marine 

 animal of the tertiary period — perhaps a connecting link between the Lacertians and 

 the Sharks, and proposed for it the name of Squalodon. 



In 1839, Dr. Harlan submitted his specimens to Professor Owen, of London, who, 

 upon a careful examination, expressed the conviction that they were not the bones of 

 a reptile, but of a great cetacean. The microscopic character of the texture of the 

 teeth, satisfactorily proved them to be mammiferous, and they were compared with 

 those of the few mammalia whose teeth are devoid of enamel. Professor Owen, with 

 his paper on the subject, has given figures of the teeth ; but subsequent specimens 

 show them to have been imperfect from the absence of the enamel and a portion of 

 the crown.* 



He found the humerus approaching more to the mammalian than to the saurian 

 types : the vertebrae were strictly mammalian and cetacean ; the teeth being freely 

 implanted in distinct sockets with double fangs, had much resemblance, in their inti- 

 mate structure, to those of the Dugong ; and he was thus induced to place it in the 

 class and order where it now remains. He says — " It is to the teeth of the Cachalot 

 and Dugong, that those of the Basilosaurus offer the nearest resemblance in the par- 

 ticulars already cited, and I conceive its position in the natural system to have been 



*Transactions of the Geological Society of London, Vol. Vf. 



