8o UNIVERSITY OF COLORADO STUDIES 



near Canyon City, but, owing to the absence of fresh- water beds from 

 most of the Cretaceous formations, they are not found between the 

 Jurassic and Laramie. The Jurassic Unios are not of distinctively 

 North American type. Omphalina?, LymncBa, Planorhis and SphcB- 

 rium are found in the Tertiary lake beds of Florissant. "» The three 

 last-named genera are still represented in the state by living species. 



This attempt to incorporate into one paper the published records 

 of our MoUusca, together with new records based upon recent collections, 

 must necessarily be more or less incomplete and in some respects inaccu- 

 rate, because of the present unsatisfactory status of some nominal western 

 species, the impossibility of now certainly determining the accuracy of 

 identification of early collections and the inaccessibility of some important 

 publications which might furnish further records or other information. 

 However, it is hoped that this bringing-together in brief form of the 

 numerous records must at least greatly aid in future investigations, and 

 afford a fresh starting-point from which our moUuscan fauna may be 

 attacked with renewed vigor, besides presenting the additional records 

 for the first time given to the public. It is quite possible that some 

 published records have been overlooked. 



The writer is very grateful to Dr. Henry A. Pilsbry and Mr. E. G. 

 Vanatta, of the Academy of Natural Sciences of Philadelphia ; Dr. Paul 

 Bartsch, of the U. S. National Museum; Mr. Frank C. Baker, of the 

 Chicago Academy of Sciences; Dr. V. Sterki, of New Philadelphia, Ohio; 

 Professor T. D. A. Cockerell, of the University of Colorado; Mr. Chas. T. 

 Simpson, of Lemon City, Florida ; and Mr. Bryant Walker, of Detroit, 

 Michigan, for their kindly assistance in the identification of difficult 

 material, for reading and revising portions of the manuscript, for 

 additional records they have furnished and for many suggestions 

 for the improvement of the paper in various ways; also to those whose 

 names are mentioned in the catalogue for the collections they have so 

 kindly brought in from various parts of the state. The records from 

 Mr. Vanatta's manuscript are based upon specimens in the collection of 

 the Academy of Natural Sciences of Philadelphia. Further collections, 



« CocKERELl,, "The Fossil MoUusca of Florissant, Colorado," Bull. Amer. Mus. Nal. Hist., Vol- 

 XXII, Art. XXVII, pp. 459-462, 1906. 



