14 THE GENUS ODOB^ENUS. 







The otner bones are described as more or less resembling 

 those of the Walrus, and do not much exceed them in size. 

 Some of them are also said to closely resemble corresponding- 

 parts of Alactlierium. 



Yan Benedens descriptions and figures of the lower jaw 

 fragment indicate features widely different from those of the 

 corresponding part in the Walrus, especially in the shortness of 

 the symphysis and in the curvature of the part represented, but 

 above all in. the number, relative size, and form of the alveoli, 

 and particularly in the large size of that of the canine, which 

 must have been almost as highly specialized as in the Sea Lions. 

 That the tusks referred to it by Van Beneden (those described 

 by Lankester especially, as well as the fragment he himself fig- 

 ures) belong here, there seems to be at least room for reason- 

 able doubt.* The differences presented by the jaw fragment 

 of Trichechodon as compared with the corresponding part of 

 Alactlierium are even still more marked. 



The more obvious characters distinctive of the three genera 

 of the Odobcenidce, as at present known, may be briefly indicated 

 as follows : 



of tlie <+cnera.\ 



1. ODOB^ENUS. Eanii of lower jaw firmly anchylosed, even in early life ; 



sympliysis short. Incisors (in adult) 0; canines 1 1: molars 3 3, the 

 last much smaller than the others. 



2. ALACTHERIUM. Kami of lower jaw not anchylosed ; symphysis very long. 



Incisors (in adult) 2 2; canines 1 1; molars 4 4, the last smaller 

 than the preceding ones. 



3. " TKICHECHODOX " (Van Beneden). Kami of lower jaw (apparently) 



unanchylosed. Incisors 1 1?, very small; canines 1 1, highly spe- 

 cialized; molars 4 4, the first small, the last three much larger and 

 suhequal. 



GENUS ODOBJENUS, Linne. 



Odolenus, LUSTSTE, Syst. Nat., i. 1735 (ed. Fe"e), 59 (applied exclusively to the 

 Walrus in a generic sense). BEISSON, Regne Aniin., 1756, 48 (used 

 strictly in a generic sense, but embracing "1. La Vache marine 

 OfZoZ>ei<s"= Walrus; "2. Le Lauiantiue Manatnx." The characters 

 given apply almost exclusively to the Walrus). 



* Van Beneden himself says : u M. Ray Laukaster avait vu en Angleterre 

 diffe'rentes grandes dents, proveuaut du crag et qui diffe~raient surtout entre 

 elles par leurs dimensions. Nous croyons devoir rapport er ces dents an genre 

 Alactherium." Yet he cites " Trlcliccliodon Intxlet/i Ray Laukaster" as a syno- 

 nym of Tricliechodon konninckii, described by himself much later! In view 

 of the uncertainties of the case, it is to be regretted that he did not propose 

 a new generic as well as specific name for his Trlcliecliodon konnincTcii. 



I With reference only to the lower jaw, the only known part, in case of 

 the extinct types, readily susceptible of comparison. 



