210 FOSSIL JAWS FROM STONESFIELD. 



tions made, have enabled him to determine the mammiferous nature of the 

 fossil. 



" Among the parts of the Basilosaurus brought to England by Dr. Har- 

 lan, 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 transversely 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 separate 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 

 simpler 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. It is evident that the pulp 

 was originally simple, but that it soon divided into two parts, from which 

 the growth of the ivory of the teeth proceeded as from two distinct centres, 

 now separately surrounded by concentric stria of growth, the exterior send- 

 ing an acute-angled process into the isthmus. The cavitas pulpi, which 

 is very small in the crown of the tooth, contracts as the crown descends, and 

 is almost obliterated near the extremity, proving that the teeth were deve- 

 loped from a. temporary pulp. 



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

 and filled with hard calcareous matter, but a transverse horizontal section 

 of the alveolar margin proves that these sockets are single, and that the 

 teeth lodged therein had single fangs. In the anterior socket, there is an 

 indication of the transverse median contraction, showing that this tooth 

 resembled in form, to a certain degree, the posterior tooth. A plaster cast 

 of a portion of the lower jaw afforded the only means of studying this part 

 of the fossil. It contains four teeth, of which the two posterior are nearly 

 contiguous, the next is at an interval of an inch and a half, and the most 

 anterior of two inches from the preceding. The last tooth is more simple 

 in form than those behind, and it has been described as a canine. This 

 fragment of the lower jaw thus confirms the evidence afforded by the frag- 

 ments of the upper jaw, that the teeth in the Basilosaurus were of two kinds, 

 the anterior being smaller and simpler in form, and further from each other 

 than those behind . 



" Mr. Owen then proceeded to compare the Basilosaurus with those 

 animals which have their teeth lodged in distinct sockets ; as the Sphy- 

 rcena, and its congeners among fishes, the plesiosauroid and crocodi- 

 lean Sauria, and the class Mammalia ; but as there is no instance of 

 either fish or reptile having teeth implanted by two fangs in a double 

 socket, he commences his comparison of the Basilosaurus with those Mam- 

 malia which most nearly resemble the fossil in other respects. Among the 

 zoophagous Cetacea the teeth are always similar as to form and structure, 

 and are invariably implanted in the socket by a broad and simple basis, 

 and they never have two fangs. Among the herbivorous Cetacea however, 

 the structure, form, number and mode of implantation of the teeth differ 



