534 BALANIDA. 
wall beyond the inner boundary of the involution from the 
Bal. definita. 1 have named this species Balena emar- 
gunata. 
In the petro-tympanic bone of the Cachalot, fig. 220, 
and the tympanic bone, fig. 225, @ is the involuted con- 
vexity ; 4, the over-arching plate; 7, outer lobe; /’, inner 
lobe; 7’, under and outer lobe; 0, Eustachian outlet; 7, 
rough outer process of the tympanic portion; p, petrous 
portion ; ¢, its deep excavation. 
If we compare the characters of the Cetotolites, which 
have been already described with the petro-tympanic, 
or its tympanic portion in the Cachalot, we find that 
that referred to the Balena affinis differs in the continu- 
ous, or even, and not bilobed under and back part of 
the involuted convexity, and in the continuation of the 
overarching wall around the inner end of the tympanic 
cavity ; it differs, in short, like the tympanic bone of the 
Balena, in its entire figure from that of the Cachalot. 
If we take the Balena definita, we find that besides the 
absence of the bilobed character of the involuted convexity, 
it differs by its well-defined anterior border. The Balena 
gibbosa, in addition to the absence of the bilobation of the 
involuted convexity, differs from the Cachalot in its limited 
extent, as well as its greater convexity in the tympanic 
cavity. 
The only Cetotolite which makes any approach to the 
peculiar characters of that of the Cachalot, is that which 
I have described under the name of Balena emarginata, m 
consequence of the vertical notch, or posterior emargination 
of the involuted convexity, which gives it a slightly bilobed 
character. It differs in a marked degree from the Cacha- 
lot, however, by the very inferior development of the lobe 
corresponding to the inner one in the Cachalot; and it 
