Exuiot SmitH, Brain of Archeocett. 45 
the sides extend upward toward the narrow dorsal surface with 
a gradual slope. In the artificial cast, however, the lateral 
parts of the hemispheres seem to be expanded into full rounded 
swellings. 
Then, again, the antero-posterior diameter of the hemi- 
sphere is much shorter (being about 13 mm. less) than it is in 
the natural cast, although the breadth of the two specimens. is 
approximately the same. It may be that the anterior parts of 
the skull, from which the artificial cast was made, are so dam- 
aged that little reliance can be placed upon the mold as an in- 
dication of the exact form of the brain. In fact, if this 
artificial cast even approximates to the form of the brain, it is 
quite certain that it did not belong to the same genus as the 
animal from which the natural cast was derived. 
In other words, as we know that the artificial cast belonged 
to Zeuglodon, the probability is that the natural cast furnishes 
the first evidence of some hitherto undescribed genus of 
Archzoceti. 
Behind the part 8, which I have just described as the 
cerebrum, there is (in the natural cast) a large, irregular mass 
of avery peculiar shape, not exactly comparable to the condi- 
tion occurring in any other brain known to me. 
Immediately behind the hemispheres (d) there is a great 
transverse bar (c) measuring 125 mm. in the transverse direc- 
tion—z.e., extending on each side 15 mm. beyond the lateral 
margin of the cerebrum (6). 
Each lateral extremity of this mass (c) is expanded to form 
a large buttress. In the natural cast these buttress-like masses 
are practically vertical, and of uniform thickness ; whereas in 
the artificial cast they are obliquely-placed, and expanded ven- 
trally. In the natural cast the mesial continuation of these 
thick lateral masses (each of which measures 30 mm. antero- 
posteriorly) becomes reduced to a bridge measuring only 5 or 
6 mm. [the exact figure cannot be stated, because a piece of 
bone (fig. 1, ¢) partially covers this region]. 
In the deep concavity behind the narrow bridge of the area 
¢ (in the natural cast) two rounded, irregular, walnut-like bosses 
