﻿INTRODUCTION. 



This work was begun immediately after the pubhcation of 

 my "Synopsis of the Naiades" in 1900 and was completed, 

 substantially as it now appears, in the latter part of 1901. It 

 was prepared in anticipation of an immediate publication with 

 illustrations of all the species. But owing to the failure of 

 that expectation and my removal to Florida in 1902, the MSS. 

 was laid aside and nothing further done upon it until recently. 



There can be no doubt but that the lack of a convenient 

 handbook of the Unionidcr, which would enable the student to 

 have adequate descriptions of all the species before him, has 

 had much to do with the comparative neglect that the family 

 has suffered, especially in this country, where it is so remark- 

 ably and characteristically developed. The literature is scat- 

 tered, expensive, largely out of print and in many cases prac- 

 tically unattainable. The necessary consequence has been that 

 the identification of nearly all of the rarer species has been 

 based upon the individual conceptions of the inore prominent 

 collectors rather than on a careful study of the original de- 

 scriptions. The resulting uncertainty and misapprehension as 

 to the correct understanding of many of the species is widely 

 prevalent among collectors and, even in the museums, there is 

 not a little incorrectly named material. 



It is with the hope of supplying, to some extent at least, this 

 deficiency that it has been deemed advisable to publish this 

 work in its present form, without illustrations. 



What we should have in this country is a fully illustrated 

 manual of the Naiades such as has been published on the land 

 and fresh-water univalves. But, unfortunately, there seems to 

 be no prospect of a publication of this kind and, in its absence, 

 it has been thoug'ht that the gathering together of descriptions 

 of all the species in a single volume would be of service to 

 those already interested in our native species and might tend 

 to excite a greater interest among those, who might be inclined 

 to collect and study them, but who have been deterred by the 

 lack of accessible literature. If this result shall be attained, 



