A REVIEW OF THE NON-MARINE FOSSIL MOLLUSCA 

 OF NORTH AMERICA. 



By C. A. White, M. D. 



INTRODUCTORY REMARKS. 



In this article I propose to review the principal known facts concern- 

 ing the fossil fresh- water, brackish-water, and land mollusca of North 

 America, taking up each family in the order of systematic classification, 

 and tracing the history of its occurrence, so far as it has been learned, 

 from the earliest known appearance of any of its species within the 

 present limits of North America until the present time; and to follow 

 the same with some general discussion of certain questions that are sug- 

 gested by the facts thus set forth. For the purpose of giving an ap- 

 proximately chronological view of the different faunae the figures are 

 arranged on the plates under headings that indicate the successive geo- 

 logical periods to which they belong. The plan proposed involves at 

 least brief mention of every species of non-marine fossil mollusca yet dis- 

 covered in North America, and the illustration of nearly all of them by fig- 

 ures, which show their external form and leading features, so far as they 

 are known. To avoid frequent repetition, it is mentioned here that all 

 statements made in this article in regard to the range of families and 

 genera in time, inust be understood as applying to North America alone, 

 unless it is otherwise expressly stated. 



The scope of this article, as indicated by the title and foregoing re- 

 marks, is a very wide one; and the presentation of such a title would 

 seem to imply the known existence of much material upon-which to base 

 a discussion of the subject. Lest I should seem to assume greater knowl- 

 edge of this subject than the facts will warrant, it may be stated that 

 while the material upon which our present knowledge of it is based is 

 really considerable and very important, it is nevertheless true that as 

 regards a continuous history of the faunae herein discussed, and the 

 geological epoch in which our most common living molluscan types 

 really originated, our knowledge is very imperfect. Enough material, 

 however, has been collected to throw much light upon the character of 

 the ancestral representatives of many of the families, which are herein 

 mentioned. It is proposed to go so far only in the discussion of these 



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