64 ODOBJSNUS EOSMARUS ATLANTIC WALRUS. 



nearly of the same size, and equally closely packed, and are 

 connected with stellate lacunae in some numbers near the peri- 

 phery of the tooth. This structure, which is not peculiar to the 

 Walrus, is, nevertheless, a test of affinity, inasmuch as the form 

 of the lacunae varies in different animals. They are not met 

 with in the tusks of the Proboscidea or the Hippopotamus, but 

 occur in the curious incisors of the Dugong. The ' dentiual 



cells 'of the Crag tusks also resemble those of the Walrus 



In structure the cement exactly resembles that of the Walrus, 

 displaying vascular canals, bone-lacunae, and canaliculi, of the 

 same form and disposition but the proportion which it bears 

 to the thickness of the other tooth-tissues appears to be larger 

 in the Walrus than in the fossil. 



"From the foregoing remarks it will be apparent that we have 

 in these fossil tusks characters which ally them most closely to the 

 large canines of the genus Trichecus." After enumerating the 

 points of form and structure which distinguish these tusks from 

 those of other animals, and those which assimilate them to those 

 of the Walrus, he thus generalizes the results of his investiga- 

 tions : " Lastly, they resemble the large canine tusks of the 

 living Tr-ichecus in their curvature, varying lateral compression, 

 large surface-furrows, short and wide pulp-cavity, globular 

 ' osseo-dentine', and every detail of minute structure. They 

 differ from them in their greater curvature at the point of the 

 tusk, their greater lateral compression, and minor development 

 of cement. 



" I accordingly propose to establish the genus Trichecodon to 

 receive the animal thus indicated. The justification of a gen- 

 eric separation must be sought in the fact of the great antiquity 

 of the Bed Crag, and the consequent probability of the associ- 

 ation of other and more distinctive attributes with those of the 

 tusks." 



As regards its geological position and associations, Mr. Laii 

 kester adds: "It appears that the Tricliecodon Huxley i, like the 



Cetacean remains of the Crag and large Sharks' teeth, 



is a derived fossil in the Bed Crag, belonging properly to the 

 Middle Crag, which is not now observable in this country [Eng- 

 land], but is well developed at and near Antwerp."* 



It thus appears that Mr. Lankester was as much, or more, in- 

 fluenced in his generic differentiation of these fossils from their 



* Quarterly Journal of the Geological Society of London, xxi 18P5 pp 

 22G-231. 



