Tertiary.] PALZONTOLOGY OF VICTORIA. [ Mammalia, 
Prats LY., Fieas. 1 anp 2. 
PHYSETODON BAILEYI (McCoy). 
[Genus PHYSETODON (McCoy). (Sub-kingd. Vertebrata. Class Mammalia. Order 
Cetacea.) 
Gen. Char.—Teeth very large, fusiform, slightly arched, circular in section; at about 
middle of length the thickness of the cement is about one-fourth of the diameter, and the dentine 
about one-half the diameter. The osteodentine of the pulp-cavity ceases at about half the 
length from the base, beyond which the dentine shows conical layers of growth coinciding 
with the form of the apex, the thick cement becoming thinner towards the point; base of the 
tooth tapering conically, more rapidly than the apex, to a narrow conical small pulp-cavity 
coinciding with the diameter of the osteodentine. External surface of cement finely sulcated 
with longitudinal vermicular irregular minute wrinkles and pits. ] 
DescripTion.—Tooth about 10 inches long and 2 inches wide at middle, taper- 
ing gradually, and slightly arched towards the obtusely rounded conical apex of the 
crown. Base tapering more rapidly than the crown to a small conical pulp-cavity 
4 lines in diameter and 8 lines deep. Thickness of cement at middle of tooth, 53 
lines. Both the dentine and cement have their outer surface marked with minute, 
wavy, rounded vermicular ridges with pits in the intervening grooves, and fewer and 
much larger faintly marked rounded irregular ridges. 
In the general form, size, and in the proportion which the cement 
and dentine bear respectively to the entire diameter at about the 
middle of the tooth, this fossil agrees with the gigantic living 
Cachalot or Sperm- Whale, the largest of which our fossil equals in 
size. Instead of the base, however, terminating in a wide conical 
pulp-cavity, with a narrow margin of tooth-tissue as in the living 
Physeter, the base of the fossil tapers to a narrow point, which 
might be mistaken for the apex of the tooth but for having a small 
conical cavity. The section of the tooth shows the osteodentine 
of the pulp-cavity with the same curious spheroidal structure as in 
Physeter, produced by the tendency of the calcigerous cells to form 
concentric layers round detached vascular irregularly scattered 
centres ; and the dentine presents the same lines converging to 
the apex as in the living form, from layers of calcigerous cells (as 
usual in cetaceous dentine). Prof. Halford has kindly measured 
for me the corpuscles as ;2;,th of an inch long and =2;;th of an 
inch wide on the average, and the tubuli about =>4,;th of an inch 
in diameter, but almost unmeasurable. The corpuscules and tubuli 
being therefore smaller than in the English crag fossil Balenodon. 
[19 ] 
