72 Mr. Owen on the Zeuglodon cetoides. 



* 



and the class Mammalia. As there is no known instance of either fish or reptile 

 having its teeth implanted by two fangs in a double socket, I shall proceed in the 

 first place to compare the above-described general and obvious characters of the 

 teeth of the Zeuglodon with those of the Mammalia which most nearly resemble 

 them in these respects,; and then point out more particularly the discrepancies 

 which, in a similar comparison, are observable in the teeth of Reptiles. 



In the true or zoophagous Cetacea, the teeth in each species resemble one an- 

 other in form and structure, and are invariably implanted by a broad and simple 

 basis in the socket, and never have two fangs. This uniformity and simplicity 

 of structure does not, however, prevail in the herbivorous section of the cetace- 

 ous order, but the species differ considerably both as to the structure, form, num- 

 ber, and mode of implantation of the teeth. 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 somewhat similar to that of the Zeuglo- 

 don, but broader, and with the opposite indentations less deeply penetrating the 

 crown of the tooth (PI. VIII. fig. 4). These teeth however, when entire, pre- 

 sent a form of the grinding surface very different from those of the Zeuglodon^ 

 inasmuch as it supports two transverse conical ridges ; while the hinder molars 

 differ still more, in having three transverse ridges. 



The Dugong presents a nearer general resemblance to the Zeuglodon in its mo- 

 lar teeth, the anterior ones being smaller and more simple than the posterior, and 

 the complication of the latter being due to exactly the same kind of modification 

 as in the hinder teeth of the Zeuglodon. The posterior molar has its longitudinal 

 diameter increased, and its transverse section also gives an approach to the hour- 

 glass figure, in consequence of the tooth being traversed longitudinally by two 

 grooves, which encroach upon the substance of the tooth from opposite sides 

 (PI. VIII. fig. 3) ; there is also in this tooth a tendency to the formation of a 

 double fang, and the establishment of two centres of radiation for the calcigerous 

 tubes of the ivory ; yet the molar teeth are not separated by wide intervals, as in 

 the Zeuglodon. 



In the scattered position of the teeth and their general size, we have an equiva- 

 lent to the extinct Zeuglodon in the Cachalot ; but the teeth in this Cetacean, 

 besides being almost confined to the lower jaw, are, as before stated, simple and 

 with single fangs. 



After a comparison of the teeth of the Zeuglodon or Basilosaur with those of the 

 true Saurians, I cannot find that they possess any one of the known dental pecu- 

 liarities of that class. For first, besides their implantation in the jaw by double- 

 fangs, they differ from the teeth of all known Saurians in their more complex and 

 various forms. 



