92 [April, 



free ends. Lower jaw intermediate in form to that of Rhinoceros and Tapirus. 

 Formula of deutition as in the hitter, viz., 



33 11 41 33 



in. c. ]}. m. t. m. = 44. 



33 1 I 44 33 



The incisors and canines are arranged in semicircles as in Tapirus^ differ 

 little in size, and have simple conical crowns. The premolars and molars resem- 

 ble those of Acerotherium incmvum. 



Hyracodon nebrascen'sis, Leidy. 



Rhinoceros nebrascensis, Leidy. Pr. A. N. S. v, 121; vii, 157; Owen's Rep. 

 Geol. Surv., Wise. 556; Anc. Fauu. Nebr. 86. 



Acerathcrium ?iebrascense, Leidy. Pr. A. N. S. v, 331. 



A unique species, possessing a greater number of teeth than any other known 

 member of the Rhinoceros family. It was about the size of the common hog. 



Locality, ilauvaises Terres of Nebraska. 



3. TiTANOTHERiUM, Leidy. 

 Formula of dentition as follows: 



22 11 44 33 



in. c. p. m. t. m. = 



? ? 11 44 33 



The molars are separated from the canines by wide intervals. The latter teeth 

 have short, robust, couoidal crowns. Outer lobes of the premolars like those of 

 Rhinoceros, the inner ones isolated from the former and connate. Outer lobes 

 of the true molars like those of Falceotherium ; the inner ones three in number, 

 of which the intermediate one is conical and is the largest, and the others are 

 triliedral, as in Chalicotherium. 



TiTANOTHERiUM Proutii, Leidy. Auc. Faun. Nebr. 72 ; Pr. A. N. S. vii, 157. 



Paloiothe.rium, Cuv. Prout. Am. Jour. Sci. Arts iii, 248. 



Palceoiheriunil Proutii, Owen, Norwood, and Evans. Pr. A. N. S. v, 66 ; Leidy, 

 Ibidem 122 ; Owen's Rep. Geol. Surv. Wise. 551. ," 



Rhinoceros 1 americanus, Leidy. Pr. A. N. S. vi, 2. 



Eolherium americanum, Leidy. Pr. A. N. S vi, 392. 



Palccotherium giganteum, Leidy. Anc. Faun Nebr. 78. 



A unique species, and one of the largest of pachyderms. Length of the upper 

 dental series in a straight line 17 inches; transverse diameter of second true 

 molar 3j inches, antero-posteiior diameter the same. 



Locality. Mauvaises Terres of Nebraska. 



Description of Twenty-five New Species of Exotic Uniones. 

 By Isaac Lea. 



Unio Hainesianus. Testji alata, laevi, subrotundata, subinflata, valde insequi- 

 laterali, valvulis crassis ; natibus prominentibus, angulatis ; epiderraide luteo- 

 fusca ; dentibus cardinalibus crassis, crenulatis elevatisque; lateralibus longis, 

 crassis subcurvisque ; margarita alba et iridescente. 



Uab. Siam. S. R. House, M. D. 



Unio Myersiancs. Testa bialata, Iffivi, triangulari, subcorapressa, inequi- 

 laterali, postice angulata ; valvulis crassis ; natibus prominulis epidermide tene- 

 broso-fusca ; dentibus cardinalibus longis creuulatisque ; lateralibus pras- 

 longis, lamellatis subcurvisque ; margarita colore salmonis tincta. 



Hub. Siam. S. R. House, M. D. 



UiVio HofSKi. Testa bialata, L-evi, triangulari, compressa, valde ina;qnilaterali, 

 postice obtuse angulatii, valvulis subcrassis ; natibus prominulis; epidermide 

 fusca ; dentibus cardinalibus lamellatis; lateralibus praelongis, lamellatis 

 subcurvis(iue ; margarita colore salmonis tincta. 



Uab. Siam. S. R. House, M. D. 



