114 POST-PLEIOCENE FOSSILS. 



Genus, CASTOROIDES.-Foster. 



CASTOEOIDES OHIO EN SIS. 

 Plate XXII. Figs. 5—8. 



Animal of the order Rodentia, Amer. Jour. Sci., XXI, 80. 



Castoroides Ohioensis, Foster, Second Rep. Geol. Surv. Ohio, 81; Hall and Wyman, Brit. 

 Jour. Nat. Hist., V, 385; Wyman, Am. Jour. Sci., 2d s. X, 62. 



Remains of this most huge of all rodent animals, according to Prof. Wyman, have been 

 discovered in New-York, Ohio, Tennessee, and Louisiana.* The cabinet of the Academy 

 of Natural Sciences, of Philadelphia, contains the greater portion ^of an upper incisor, 

 two upper molars, and two petrous bones of this animal, which were obtained in digo-ino- 

 a well, forty feet below the surface, near Shawneetown, Illinois. In Plate XXII, figure 5, 

 is represented the upper incisor above referred to. 



Prof. Holmes' collection contains a small fragment of an incisor and of an upper molar 

 tooth, from the Post-Pleiocene deposit of Ashley river. 



Though the skull of Castoroides resembles that of the Beaver, the teeth differ totally 

 in their form and constitution. The molar teeth of the former are constructed upon the 

 same plan as those of the Capybara, consisting of a series of flat columns of dentine 

 invested with enamel and held together by cement. 



The upper incisors in section form a half ellipse with the plane inward. The antero- 

 external convex surface is invested with thick and strongly fluted enamel, and the 

 posterior surface is smooth and concave. The cutting extremity of these teeth is worn 

 away as in the Musk-rat, that is to say into a deep depression on the inner side of the 

 beveled surface. The lower incisors are trilateral in section, the inner and posterior sides 

 smooth and slightly depressed, and the anterd-external surface convex and invested with 

 enamel as in the corresponding upper teeth. 



The fluting of the enamel surfaces of the incisors extends in a well-marked manner 

 into the dentine. 



* Amer. Jour. Sci., 2d s. X, 64. 



