528 BAL^ENID.E. 



including the Grampus and Hyperoodon, in having the 

 hinder extremity of the bone simple and not bilobed ; and 

 some of them differed, also, in having the anterior outlet 

 of the cavity partially enclosed by the extension of the 

 outer plate around that end. 



With regard to the Cachalot (Physeter), I had not had 

 the opportunity of comparing the Felixstow fossils, when 

 I first gave an account of them, with the tympanic bone 

 in that genus, which I then knew only by the figures given 

 by Camper * in his characteristic but sketchy style. 

 Cuvier, who founds his notice of the tympanic bones of 

 the Cachalot on the same figures, states that they most 

 resemble those of the Delphinidee ; but are less elongated 

 and less bilobed posteriorly .-f* The figures show still more 

 clearly that the tympanic cavity is continued freely forward 

 out of the anterior end of the bone, and terminates by a 

 relatively wider outlet than in the DelphinidtE.^ 



The idea thus given of the form of the tympanic bone 

 of the Cachalot, being, as I have since had the opportunity 

 of satisfying myself, in the main correct, the comparison of 

 most of the Cetotolites becomes limited to the true whales 

 (Balanidte), in the few known species of which the dis- 

 tinctive characters of the tympanic bones are afforded by 

 their relative size and the shape of their inferior surface. 



In Baltenoptera the tympanic bones, according to Cuvier, 

 are very small in proportion to the head, and are equally 

 convex at their inferior surface. 



* ' Anatomie des Cetaces,' Pis. xxiii. xxv. 



) ' Ossemens Fossiles,' 4to., v. pt. i. p. 376. 



J Cuvier, (Leqons d'Anatomie Comparee, ed. 1799, vol. ii. p. 492,) says, 

 generally : " L'extremit6 anterieure de la caisse cst toute ouverte :" which cha- 

 racter, M. Adrien Camper thinks he meant to apply to the Cachalot more par- 

 ticularly. I shall combine the description of the petro- tympanic bone of the Ca- 

 chalot, which I have recently received, with that of the Cctotolite most resembling 

 it. 



