EASTMAN : sharks' TEETH AND CETACEAN BONES. 97 



and the existing H. rostratus are as follows : The posterior articular 

 facette of tlie periotic is more deeply concave in the deep-sea specimens, 

 the " accessory ossicle " (p)vr. tubarius) is relatively smaller and 

 scarcely inflated, the channel for the Indlopian canal on the tympanic 

 aspect is less distinctly marked, and the promontory, or capsule con- 

 taining the semicircular canals, is less expanded. Some minor differ- 

 ences are also to be observed in the relative size, arrangement, and 

 direction of the apertures seen on the cerebral side of the periotic. 

 The involucrum of the tympanic is not serrated, although the corres- 

 ponding part in the living species displays as many as six or seven 

 prominent denticles. Two specimens each of the periotic and tympanic, 

 dredged from three different stations, are represented in Plate 2, Figs. 

 33-36. 



Peculiar markings of certain deep-sea ear-hones. It deserves mention, 

 in conclusion, that none of the ear-bones dredged by either of the 

 " Albatross " Expeditions show any indications of surface markings 

 comparable to those observed in two specimens, belonging respectively 

 to the right and left sides, of Balaenine tympanic bullae brought up 

 from one of the " Challenger " stations (No. 286) in the South Pacific. 

 As the bullae are of corresponding form and proportions, and are stated 

 to exhibit similar markings, it is extremely probable that they belonged 

 to a single individual, and that their incised lines are a natural feature, 

 rather than tlie result of post-mortem injuries. A certain amount of 

 regularity is to be observed in the disposition of the grooves. They are 

 not distributed at haphazard, nor do they intersect one another at 

 varying angles, as we should expect them to were they of accidental 

 origin. Furtliermore, the bone substance is so exceedingly hard and 

 dense that a knife-blade makes no impression upon it ; only with the file 

 is an incision possible. Yet it has been suggested that the inden- 

 tations noticed in the " Challenger " ear-hones were caused by sharks' 

 teeth. This conjecture was first advanced by J. Thoulet,^ and an 

 attempt to lend some color of probability to it was made later by A. 

 Portis.'^ 



The authors of the volume on Deep Sea Deposits of the " Challenger " 



1 Thoulet, J., Les depots sous-marins. Rev. Scient., (1892), 50, p. 105. 



2 Portis, A., Un Dioplodonte nel pliocene astigiano. Rev. Ital. di Paleont , 

 (1897), 3, p. 34-39. Consult also the earlier memoir of the same author entitled 

 " Nuovi studi' sulle traccie attribuite all' uomo pliocenico." Mem. R. Ace. Soi. 

 Torino, ser. 2 (1884), 35, p 327-354. In Plate 1 Fig. 1 of this memoir is shown a 

 tooth of Carcharodon angustidens actuail}- embedded in a vertebra of Halitherium, 



VOL. L. — No. 4 7 



