118 



32. Valvata parvula, Meek and Haydeu. 



33. Melania oninutula, Meek and Hayden. 



34. 3Ielania Antfionyi, Meek and Hayden. 



35. Melania multistriata, Meek and Hayden. 



36. Melania Nebrascensis, Meek and Hayden. 



37. Melania Warrenana, Meek and Hayden. 



38. 3Ielania tenui carinata, Meek and Hayden. 



39. Cerithitim Nebrascensis, Meek and Hayden. 



The tertiary basin of White and Niobrara rivers forms one of the 

 most interesting and remarkable fresh water deposits on our continent. 

 It differs, both lithologically and paleontologically, from the two 

 basins previously alluded to. It contains no fossil plants, no lignite 

 beds, and not one of the numerous species of organic remains which 

 have been collected from it is identical or allied to species found in 

 other portions of the tertiary of the northwest. Two distinct faunas 

 are represented by the collections from this deposit. The fauna of the 

 miocene period from the region of White river, and the fauna of the 

 pliocene period from the Niobrara. The latter fauna has enabled Dr. 

 Leidy, the distinguished comparative anatomist, to arrive at some 

 important conclusions. He says : 



" The extinct fauna of the Niobrara is especially rich in remains of 

 ruminating and equine animals. Among the former are several pecu- 

 liar genera, of which two are closely allied to Oreodon and Leptauche- 

 oiia, of the miocene deposit of the Mauvaises Terres; one is allied to 

 the musk-deer and another closely approaches the camel. Besides the 

 remains of a true species of JEquus, the collection contains those of two 

 species oi Hipparion, and several peculiar genera of the equine family. 

 There are also remains of several species of canine and feline animals, 

 of a small species of beaver, and of a species of porcupine more nearly 

 allied to that of the old world than to our own recent one. The col- 

 lection further contains remains of a rhinoceros, resembling those of 

 India, those of a new species of mastodon, and those of a large 

 elephant. 



" One of the most remarkable circumstances in relation with this 

 extinct fauna is, that it is more nearly allied to the present recent one 

 of the old world than to that of our own continent. From a com- 

 parison of our recent fauna and flora with that of the eastern continent, 

 the deduction has been made, that the western continent is the older 

 of the two, geologically speaking, whereas, the Niobrara fauna would 

 indicate just the reverse relationship of age. A number of similar 

 instances show that totally different fauna and flora may be cotempo- 

 raneous, and do not necessarily indicate different period of existence." 



