Geological Society, 211 



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. 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 fur- 

 ther from each other than those behind. 



Mr. Owen then proceeds to compare the Basilosaurus with those 

 animals which have their teeth lodged in distinct sockets, as the 

 Sphyrsena, and its congeners among fishes, the Plesiosauroid and Cro- 

 codilean 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 Mammalia which most nearly resemble the fossil in other 

 respects. Among the zoophagous Cetacea the teeth are always si- 

 milar 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, num- 

 ber and mode of implantation of the teeth differ considerably. In 

 the Manatee, the molars have two long and separate fangs lodged 

 in deep sockets, and the anterior teeth, when worn down, present 

 a form of the crown similar to that of the Basilosaurus, but the 

 opposite indentations are not so deep ; and the entire grinding sur- 

 face of the molars of the Manatee differs considerably from those of 

 the Basilosaurus, the anterior supporting two transverse conical 

 ridges, and the posterior three. The Dugong resembles more nearly 

 the fossil in its molar teeth ; the anterior ones being smaller and 

 simpler than the posterior, and the complication of the latter being 

 due to exactly the same kind of modification as in the Basiloraurus, 

 viz. a transverse constriction of the crown. The posterior molar 

 has its longitudinal diameter increased, and its transverse section 

 approaches to the hour-glass figure, produced by opposite grooves. 

 There is in this tooth also a tendency to the formation of a double 

 fang, and the establishment of two centres of radiation for the calci- 

 gerous tubes of the ivory, but the double fang is probably never com- 

 pleted. The teeth in the Dugong moreover are not scattered as in 

 the Basilosaurus. 



Mr. Owen then briefly compared the teeth of the fossil with 

 those of the Saurians, and stated that he had not found a single 

 instance of agreement in the Basilosaurus with the known dental 

 peculiarities of that class. From the Mosasaurus the teeth of 

 the American fossil differ in being implanted freely in sockets and 



q2 



