86 INVERTEBRATE PALEONTOLOGY. [WHITE. 



responds with the description of P. Utahensis Meek. The Vivipanis and 

 Goniobasis I have, in the following catalogue, referred respectively to F. 

 paludinceformis Hall sp. and G. tenera Hall sp. Goniobasis nodiilifera Meek 

 ( Cerithium nodidosum Hall) and G. Carteri Conrad, are regarded as syno- 

 nyms of G. tenera; and from among the thousands of examples that have 

 been collected from the strata under discussion, it would be easy to make 

 selections that, if found separately, would be taken to indicate an equal 

 number of species, as different from those as they are from each other. 

 Fortunately, however, the specimens in all cases are so abundant that other 

 selections may be made showing full intermediate gradations between all 

 the species that have been, and doubtless all that may yet be, proposed from 

 among them. 



The character and extent of the variations of these species in their 

 geographical distribution, vertical range, and local association will be dis- 

 cussed in a future report. It is, therefore, sufficient now to suggest that 

 these forms will present some of the best opportunities for the zoologico- 

 historical study of certain species through a great lapse of geological time 

 that paleontology has ever furnished. 



This remarkable uniformity of molluscan types through all the groups, 

 together with their almost exact identity with recent types of fresh- water 

 mollusca, seems at first view to present an argument against the supposition 

 that those Cenozoic deposits occupied the whole of Tertiary time, when con- 

 sidered only in relation to the invertebrate remains ; but the slight value of 

 fresh-water molluscan forms in such generalizations has already been shown. 

 If relied upon at all, their modern aspect would seem to indicate late Ter- 

 tiary time only, while, on the other hand, the physical connection tff the 

 lowest group with the uppermost group of Cretaceous strata is such as to 

 leave no doubt that the former represents the earliest epoch of Tertiary time. 



Besides this several of the species found in the brackish-water layers 

 at the base of the Bitter Creek Group are closely related to species found 

 in similar deposits in Slavonia and referred to the Eocene Tertiary by 

 Brusina.* (See "Fossile Binnen-Mollusken aus Dalmatien, Kroatien, und 

 Slavonien von Spiridion Brusina, Agram, 1874.") 



* It is mi interesting fact that these collections of Tertiary fresh water niollusks iu Slavonia possess 

 many Unione and Vivipariue forms that arc of living American, and not European types, while all the 

 American fossil fresh water forms with which I am acquainted are of American recent types. 



