534 



wall beyond the inner boundary of the involution from the 

 Bal. definita. I have named this species Baleena emar- 

 ginata. 



In the petro-tympanic bone of the Cachalot, fig. 220, 

 and the tympanic bone, fig. 225, a is the involuted con- 

 vexity ; 5, the over-arching plate ; ?, outer lobe ; I', inner 

 lobe ; I", under and outer lobe ; o, Eustachian outlet ; r, 

 rough outer process of the tympanic portion ; p, petrous 

 portion ; e, 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 Balana qffinis 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 

 Balcena, in its entire figure from that of the Cachalot. 



If we take the Baleena definita^ we find that besides the 

 absence of the bilobed character of the involuted convexity, 

 it differs by its well-defined anterior border. The Balaena 

 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 Baleena etnarginata, in 

 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 



