230 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 8, 



** osseo-dentine," was about as 3 : 1. In structure the cement ex- 

 actly 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 Tricliecus. It will perhaps be well to 

 enumerate the points of form and structure which distinguish them 

 from the tusks of other animals, and those which assimilate them to 

 the canines of the Wah'us. 



1. They are distinguished from the Proboscidean tusks generally 

 by their lateral compression, slight curvature, and deep superficial 

 groovings, and by the absence of that cylindrical form, smooth sur- 

 face, and great curvature, which is present in Proboscidean tusks. 

 Structurally by the presence in the fossil tusk of a large core of 

 peculiar globular " osseo-dentine," by the presence of stellate lacunae 

 in the dentine, by the size and form of its tubes, and by the amount 

 and structure of the cement ; and by the absence of peculiar " en- 

 gine-turning," or '' guillochis," which marks the ^ivory of the Pro- 

 boscidea. 



2. They are distinguished from the tusks of the Dinotherium in 

 particular, by aU the above-mentioned characters but the last ; to 

 which may be added the absence of a deep conical basal pulp-cavity, 

 observed in the tusks of Dinotherium and of the Elephants and 

 Mastodons also. 



3. They are distinguished from the tusks of Sirenia, which re- 

 semble somewhat those of the Walrus, by their definite form, groov- 

 ing, and curvature; by their much larger core of osseo-dentine, 

 and by their short and wide, instead of elongate and angular, pulp- 

 cavity. 



4. From the tusks of Hippopotami they are distinguished by 

 every character of form and structure, the fluting of the dentine 

 (recalling the markings on the surface of the canine of Hippopota- 

 mus) being the only similarity between the two. 



Lastly, they resemble the large canine tusks of the living Trichecus 

 in their curvature, varying lateral compression, large surface-fur- 

 rows, 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 Tncliecoclon to receive 

 the animal thus indicated. The justification of a generic separation 

 must be sought in the fact of the great antiquity of the Red Crag, 

 and the consequent probability of the association of other and more 

 distinctive attributes with those of the tusks. The name Triche- 

 coclon was proposed to the author by M. Yan Beneden, as one aptly 

 describing all that we at present do, and probably ever shall, know 

 of this animal. In searching for a specific title, I have thought that 

 I cannot do better than dedicate this somewhat interesting form to 



