1856.] 89 



CETACEA HERBIVORA. 



3. TscHYROTHERiUM ANTiQUUS, Leidy. 



This genus and species are proposed upon numerous fragments of bones, con- 

 sisliugottwo vertebral bodies, the half of h ihinl specimen, several transverse pro- 

 cessi^s, and portions of ribs, discovered ny Dr. Hayden, in an out-Iyer of a lignite 

 formation, between the Moreau and Grand rivers, Nebraska. 



The bones are as dense and heavy as those of tUaiiutin-, to which the genus ap- 

 pears to be most nearly allied. The vertebral bodies, apparently posterior dorsal, 

 are transversely oval in outline, and are perforated at the sides and lower pan 

 by large canals converging towards their centre. The anterior and posterior 

 articular surfaces are slightly depressed, as are also the sides of tht body. The 

 upper part of the latter, on each side of the position of the spinal canal, presents 

 a large, rujfged concavity, about an inch and a quarter in diameter, aj jiarently 

 for articnlating with the transverse processes. These latter are antero-posieriorly 

 flattened, cylindrical and curved. Their vertebral extremity is furni^h^d with a 

 convex rugi^ed surface, corresponding to the concavities on the vertebral bodies, 

 and above this surface is a smooth one forciing the side of the ventbral canal, 

 and overhung by an abutment fv the articular and spinous processes. 



The ribs are cylindroid and tapering towards the broken ends of the speci- 

 mens, and they are quite as uense in structure as those of Manafus. 



Length of vertebral bodies ... 1^ inches. 



Transverse didineter of do. . . . 2f " 



"Vertical do. do. . . . 2 " 



RODENTIA. 



4. Steneofiber nebeascensis, Leidy. 



This species is established upon several specimens, consisting of a much mu- 

 tilated skull and several fragments of upper a'ld lower jaws with teeth. The 

 skull i^ppears to have the same form as that of Steneofiber viciacensis, but is be- 

 tween a fourth and third less in size. The dental formula is the same as in the lat- 

 1 1 44 



ter, that is, in. m = 20. The molar teeth resemble those of S. 



1_1 44 



viciacensis. 



L-^ngth of skull of <S. nebrascensis . 2J inches. 



Length of lower jaw .... If " 



Len^iili of u(>per malar series ... 7 lines. 



Length of lower molar series . . . 8 " 



From the valley of Wuite River, Nebraska. 



5. IsCHYROMYS TYPUS, Leidy. 



A new genus and species estatlished upon the greater portion of a skull and 

 two fragmeais of lower jaws. Tbe cranium bears considerable resem- 

 blance of form to that of Steneofiber. Foriuula of dentition as follows : 

 1 1 55 



in. m. = 22. The molars have cuboidal crowns and are in- 



11 44 

 serte I by distinct fangg. The upper ones bear some resemblance to those of 

 Aretomy ; but the lower ones are more like those above. 



Esnmated length of skull . . . 2| inches. 



Length of upper molar series ... 7^ lines. 



Length of lower molar series . . . 8 "} 



From the Bad Lauds of Nebraska. 



6. Palabolagus Haydeni, Leidy. 



The genus and species are founded upon numerous small fragments of jaws, 

 containing molar teeth, of a rodent allied to the Hires. The formula of the 



6 6 



molar dentition is the same as in the latter, . The molars are con- 



55 



