25 
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 irreguiar, rounded lobes jomed 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 striz of growth, the exterior 
sending an acute-angled process into the isthmus. The cavitas 
pulpi, which is very small im the crown of the tooth, contracts as the 
crown descends, and is almost obliterated near the extremity, proving 
that the teeth were developed 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 af- 
forded the only means of studying this part of the fossil. It con- 
tains 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 an- 
terior of two inches from the preceding. The last tooth is more sim- 
ple 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 fragments 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 proceeds to compare the Basilosaurus with those 
animals which have their teeth lodged in distinct sockets, as the 
Sphyrzena, 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 
