82 BULLETIN: MUSEUM OF COMPAEATIVE ZOOLOGY. 



Cetacean tooth corresponding in size to Hyperoodon, more or less 

 chocolate-colored. 



Station 4740, depth 2422 fathoms. — 1 splendidly preserved Carchar- 

 odon tooth, shown in PI. 2, Fig. 23, from the external face ; 1 Kogia, and 

 2 Delphinoid ear-bones. 



SYSTEMATIC ACCOUNT OF THE REMAINS. 



Elasmobranchii. 



(Plate 2.) 



The collection contains one hundred and thirty-three sharks' teeth, all 

 referable to three genera of Laninidae, Lamna, Oxyrhina, and Carcharo- 

 don, named in order of their numerical abundance. None of the teeth 

 are preserved in anything like their entirety. The dentine has been dis- 

 solved awa}', leaving only a thin shell of enamel, and the loss of the root 

 and lateral denticles (in all cases where the latter were formerly present) 

 is a serious hindrance to accurate determination. It has not been possi- 

 ble to recognize hei-etofore more than two species with certainty, Oxy- 

 rhina crassa Ag., and Carcliarodon megalodon Ag., both of wliicli are 

 widely distributed in Tertiary formations, but unknown in the modern 

 fauna. To this number may now be added with some degree of confi- 

 dence a third species, which we take to be identical with Carcliarodon 

 lanciformis Gibbes. These teeth are characterized by having very much 

 flattened crowns, broadly triangular in form, with acutely pointed apex 

 and finely serrated lateral margins (Plate 2, Figs. 19-22). They are 

 readily distinguished from C. megalodon by their great lateral compres- 

 sion and usually smaller size. Their separation from the existing C. 

 rondeletii is less easy, differential characters being found in the presence 

 or absence of lateral denticles, and the form of the coronal apex. These 

 three species which we are able to recognize with tolerable certainty in 

 deep-sea deposits, namely, Oxyrhina crassa, Carcharodon inegalodo7i, and 

 C lanciformis, likewise occur associated with one another in the Phos- 

 phate beds of South Carolina and other Tertiary localities. 



Illustrations of a selected series of sharks' teeth from the Eastern 

 Tropical Pacific are shown in Plate 2 of this Bulletin. As the features 

 presented by the newly acquired shark material are essentially the same 

 as have already been described at sufficient length in the " Challenger " 

 and " Albatross " Reports, no good purpose would be served by mere 

 repetition of details in the present paper. Contrariwise, the earlier 

 Reports contain only a meagre account of Cetacean ear-bones,^ hence we 



1 Some of the generic determinations in the previous Reports are clearly open 

 to question. In particular, Kogia and Globicephalus have been confused. 



