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PREFACE. 



IN preparing this list of the mollusca of Muscatine County, we 

 have not thought it desirable to attempt descriptions of well- 

 known species. Where some marked variation or some peculiar- 

 ity has appeared, that seemed to us likely to be of interest to 

 conchologists, and that would serve as guides to those students 

 and collectors who come after us, we have put it on record. The 

 size, and in some instances the weight, we have given, since it is 

 certain that the conditions under which the mollusk lives exert 

 a marked influence upon these, as well as the form and color. 



All the forms catalogued by us are in the cabinet of the presi- 

 dent, F. M. Witter ; and he has collected all the shells given in 

 our list. We therefore feel certain that no stray shells have crept 

 in from our exchanges. 



Much might have been said concerning many species of our 

 Unionidce, but we found it necessary to write somewhat according 

 to our purse. We do not see why the length of a shell should 

 always be less than its breadth. In giving the measurements 

 in the families Unionidce and Oorbiculadce, we use the terms 

 "length," "breadth," and "diameter" as follows: when the 

 shell is placed in the position it occupies when travelling, the 

 greatest horizontal space it fills we call its length, and the greatest 

 space filled at right angles to this, and vertical, we call its 

 breadth; and, when the shell is placed on its side, the greatest 

 height in this position we call its diameter. We regard the shell as 

 having three axes, all at right angles to each other : therefore, in 

 any shell that is a sphere, these will be equal. All measurements 

 of shells are from examples found in this county or vicinity, unless 

 otherwise specified. We have measured the largest, and, where 

 a great difference existed in the size of the mature shell, we have 

 also given the smallest. We have followed an alphabetical order 

 in the family Unionidce. 



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