8 INTRODUCTION. 



closely adhered to, as in leaving blank tbe " Georgia" column when 

 specimens had been collected only in South Carolina and East Florida, 

 with no data for the intermediate stretch of coast. This will show the 

 real gaps in our knowledge of the distribution, and it is to be hoped 

 will stimulate local students to fill them up. 



The extreme northern and extreme southern range are generally 

 given. When a species has been obtained off shore, smd at one locality 

 only, the extreme is usually noted in one column only, with a leaning 

 toward the northern column when the species is supposed to be a south- 

 ern form and to the southern column when it is thought to extend from 

 the colder area. These assignments must often be conjectural, but when 

 clearly understood they should not be in any way misleading. 



There are many unidentified species from this region in the National 

 collection, a large proportion of which may prove to be new. In such 

 cases the insertion of their distribution, as far as known, may lead to 

 fuller investigation by collectors, though no specific name can be ap- 

 plied to them in the catalogue. 



When a species whose name appears in one of the cited publications 

 is not found in this catalogue, or is not cited from the locality to which 

 the published authority refers it, the reader may infer that either the 

 prior identification is here regarded as inaccurate, or, more generally, 

 that the prior name is not entitled to be used. 



In many cases the full explanation for such changes will be found in 

 the Report on the Blake Mollusca, but in the present catalogue it has 

 been quite impracticable, as well as undesirable, to attempt any syn- 

 onymy. 



The writer has attempted to steer a middle course between overdiv- 

 ision of large natural groups and the conservatism which confounds 

 unlike things together. It is not to be expected that his decisions will 

 be universally acceptable or satisfactory, since there are " many men, 

 many minds" in biology as well as worldly affairs. 



In practice, to be a good systematic malacologist requires much study 

 and a wide knowledge of the literature. It is no longer possible in 

 systematic conchology for a student to acquire facility without a good 

 library and long practice. One may be a good naturalist and do valu- 

 able work for science, however, without being a systematist, and the 

 field of work is so vast that the earnest worker may keep himself em- 

 ployed in almost any district south of Sandy Hook. The writer has 

 found a reasonable amount of subdivision of the familiar genera of use 

 in clear thinking and in endeavoring to formulate accurately the facts 

 of nature. Subgenera and sections have therefore been introduced into 

 the catalogue, to be used or discarded as the reader may prefer. 



Some groups have been pretty thoroughly investigated and the sub- 

 divisions may be named with confidence, and have therefore been 

 inserted. In other cases a thorough revision is yet to be made and the 

 subdivisions can not be named with confidence, and, therefore, are to a 



