Cope.] i"^-' [July 1(5, 



Width distally 0325 



" least 0270 



" proximally 0320 



" of distal alveolus 02 



" of second " 65 



This species was fouud with a number of rolled fragments of Mastodon 

 not far from Savannah, Georgia. The specimen is silicified, is dense and 

 heavy, and slightly woni. Its color is black, and it i-esembles in all 

 respects the remains of the Mastodon accompanying. It is preserved in 

 the Museum of Comparative Zoology, Cambridge, Mass, and was lent 

 me for exaipination by Prof. Agassiz, the director. 

 Hemicaulodon, Cope. 



This genus is established on a right upi^er incisor of a large Sirenian 

 Mammal allied to the Dugong. 



The form of the tooth is that of a compressed, slightly curved cylinder, 

 with distal and proximal vertical diameters equal. There are two open 

 grooves on the inner and one similar on the outer side, the former enclos- 

 ing a broad bead. The transverse diameter posteriorly is less than that 

 anteriorly. The substance of the tooth is composed of a large axis of 

 osteo-dentine surrounded by a broad cylinder of dentine, which is in turn 

 surrounded by a thick stratum of cementum . The dentine is marked at 

 regular distances by annuliform ridges, which are more or less undulate. 

 They become gradually more distant distally. These ridges can be traced 

 through the cementum. The cementum is everywhere entire, and is 

 thicker distally. It presents externally a few longitudinal grooves at ir- 

 regular distances, and numerous fine striffi irregularly disposed. 



The pulp cavity is small and compressed; how far it extends into the 

 shaft is uncertain, as it is choked by hard debris; biit at the lowest point 

 it is much contracted and sublinear. But a portion of the triturating 

 surface is preserved; it truncates the tooth upwards and backwards in 

 relation to its axis, as would be anticipated in a superior incisor. 



The characters of this genus ally it to Halicore and Rhytiodus Lartet. 

 In Trichechodon Lankester, the dentine does not present tlie external 

 transverse ribs; the same character distinguishes it from Halitherium 

 Kaup; in both these genera there is a distal acumination not visible in 

 Hemicaulodon. Ontocetus Leidy from the Miocene of North Carolina, 

 which I suppose to be a large Sirenian allied to Halicore, presents very 

 weak and a,pproximate dentinal ridges on part of its surface. It differs 

 from this genus in the acuminate form of the tooth, and it probably pre- 

 sented a conic apex as in Trichechodon. 



The comparison with its nearest allies is as follows. Both Halicore and 

 Ehytiodus have the upper incisors dilated and flattened distally, and Avitli 

 a narroAv oblique triturating surface. This extremity is, according to 

 Owen, the only portion of the tooth wliich is exposed beyond the gum. 

 In the present genus no such expansion exists so far as observed, and the 

 truncation and exposure of the tooth, takes place at a point which would 

 correspond to the basal third of the fang in those genera. In tlic latter 



