52 PROCEEDINGS OP THE ACADEMY OP [1883. 



ON A NEW EXTINCT GENUS OF SIRENIA, FROM SOUTH CAROLINA. 

 BY E. D. COPE. 



Mr. Gabriel Manigault, the accomplished director of tlie Museum 

 of the University of South Carolina, at Charleston, has placed in 

 m}^ hands for determination an interesting fossil of that region. 

 It is the greater part of the right premaxillary bone of a large 

 sirenian mammal, containing the large incisor tooth or tusk char- 

 acteristic of the genus Halitherium. It, however, exhibits the 

 peculiarity of possessing, exterior to this tusk, a second large 

 tooth, which is probably also an incisor. This character distin- 

 guishes the form generically from other members of the order. 

 In Prorastomus Owen, tliere are an inferior incisor and a canine 

 not of sirenian type, but probably no superior incisors, or if 

 present, they are minute and conic. I propose that tlie genus be 

 named Dioplothei^ium. The only form with which it is necessary 

 to compare it is Hemicaulodon Cope,' the number of whose incisor 

 teeth is unknown. The one from which the genus is known, has 

 a dense external sheath of cementum, which is wanting from the 

 present genus. 



The color of the specimen indicates that it belongs to tlie blue- 

 gra}' marl of the Carolinian (Heilprin) miocene of our Atlantic 

 region. It has, however, been exposed to the action of the water 

 of a later sea, as it carries the bases of several Balani. 



The premaxillary bone differs from that of the Halitherium 

 minor Cuv. {H. xerreM Gerv.) and H. capgrandi Lart,, in the 

 much shorter sympliysis. The nareal border is also shorter, 

 judging from the position of the maxillar}^ suture, which is 

 further anterior than in the species named. The nareal border is 

 rounded and thickened, so as to overhang its lateral face at the 

 maxillary suture. The alveolus of the second incisor is large, and 

 is in close proximity to that of the first. Its posterior wall is 

 lost. Its fundus reaches to tlie maxillopremaxillary suture, but 

 as its anterior wall is entirely premaxillary, the tooth is probably 

 an incisor, and not a canine. 



The anterior Incisor is a tusk of flattened form, with a slight 

 taper from base to apex, and a narrow diamond-shaped section. 



' Proceedings Amer. Philos. Soc, 18G9, p. 190. 



