18 GENERAL OBSERVATIONS. 



fully represented. The collections were made at somewhat widely-separated 

 localities in Nevada and Utah. I have referred the species to the Jurassic 

 period without hesitation in allcases where they were identical, or associated 

 with species hitherto described by Mr. Meek, or Meek and Hayden, and 

 referred by them to that period. AYith the exception of one crinoidal species, 

 the fauna of the collections is wholly molluscan. 



• CRETACEOUS PERIOD. 



Next to the Carboniferous period, the Cretaceous is represented in the 

 collections by the greatest number of species. These were obtained at 

 various points in New Mexico, Utah, and Colorado. For want of available 

 data, no attempt has been made to refer them respectively to the different sub- 

 divisions of the Ci'etaceous group that have been recognized in Western 

 North America by various geologists ; but they are all regarded as clearly 

 referable to the • Cretaceous period. Although individuals of most of the 

 species are numerous, it is interesting to observe the restrictions of zoological 

 diversity which the collections, consisting of thirty-two species, present. For 

 example, the Protozoa and Radiata are entirely wanting ; the Articulata rep- 

 resented by a single species of Serpula only; and all the remainder are 3£ol- 

 lusca. Of these, the Molluscoidea are represented by a single species of 

 Lingtda; thirteen species are monomyarian Conchifera ; five, dimyarian 

 Conchifera ; nine, Gasteropoda ; and four, CeplmJopoda. 



CENOZOIC. 

 TERTIARY PERIOD. 



The collections contain fifteen species from strata at different localities 

 in Utah that I have assigned to the Tertiary period, all of which, except one 

 species of Oi/pris, are either fi'esh-water or land moUusks, mostly the former. 

 Three species are Conchifera, and of the remaining eleven species five are 

 pulmonate Gasteropods, an order that is not represented in any of the other 

 collections. 



If I were left to rely upon the zoological types alone which the fossils 

 of this small collection present, I should have no hesitation in referring them 



