530 BALUNID.!. 
the tympanic bone of the Balena mysticetus and Bal. ant- 
arctica, since the condition of the fossils would not ad- 
mit of the application of those differences in the deter- 
mination of their affinities. 
Fig. 221. 
Tympanic bone of Balena affinis, } nat. size. Felixstow. 
One of the most complete of the fossil tympanic bones, 
which measures five inches in length, resembles the Bal. 
antarctica in the slight elevation of the outer part of the 
involuted convexity (@), and its gradual diminution to the 
Eustachian end of the cavity (0): it resembles both Balane 
in its traceable continuation to that end, and in the gradual 
continuation of the concave outer wall (4) from the involuted 
convexity ; this convexity is indented also, as in both 
recent Baleene, by vertical fissures narrower than the mark- 
ed indentation which distinguishes the Bal. mysticetus : 
these fissures are almost worn out by friction in some of 
the specimens. The more perfect one under consideration 
is not, however, identical with the Bal. antarctica. 
The upper surface of the bone maintains a more equable 
breadth from the posterior to the anterior end, the outer 
angle of which, being well marked in the fossil, is rounded 
off in the recent specimen ; the under and outer surfaces of 
the tympanic bone meet at an acute angle. The above 
