X THE CHICAGO ACADEMY OF SCIENCES. 



The bibliography includes every reference to the species under 

 discussion, which the writer has been able to secure. When the 

 species has been cited erroneously under another name, that fact is 

 stated, if known. The descriptions of the shells have been made as 

 full as possible; it will be noted that the measurements of the spire 

 includes that portion of the shell from aperture to apex, in this re- 

 spect differing from those of many writers, who included in the spire 

 all but the body whorl. Measurements are given of several speci- 

 mens from different localities. It is believed that the location, number, 

 and catalog entries of the types will prove of value to future students 

 of the family. The same is true of the type locality which is given 

 in each case. With few exceptions, the types of all American Lymnseas 

 have been seen and examined. The descriptions of the anatomical 

 features have been made with great care; each drawing represents the 

 combined examinations of many different individuals in order to check 

 the results. No great difference was found in the genitalia at dif- 

 ferent seasons of the year. The organs, when at rest, appeared the 

 same in the breeding as in other seasons. The figures of the radulae 

 have been made with exceptional care as the cusps are difficult to see 

 and errors are easily made. 



The distribution maps, both recent and fossil, are arranged by 

 means of symbols to show at a glance the range of the species in the 

 different river systems. The large symbols represent actual records 

 while the small dots indicate the probable range of the species. Records 

 outside these areas are to be viewed with suspicion until verified by 

 competent malacologists. The list of records is arranged alphabetically 

 by states and will doubtless be found of use to those malacologists 

 who may be working up state lists. In a few cases (palustris, stag- 

 nalis, etc.) it has not seemed necessary to include these records, as the 

 species are universally distributed over a large area. Under ecology 

 is given all available information concerning the habitat relations of 

 the species. This is a subject which has received scant attention and 

 there is a wide field for excellent work in this direction. Large col- 

 lections should be made from restricted areas and exact notes on 

 habitat relations as well as photographs should be secured. Much light 

 will be thrown on the exact relationship of several obscure species by 

 studies of this kind. Under remarks considerable information is 

 given concerning the species as well as comparative notes indicating 

 the specific or varietal differences. The figures on the plates illustrate 

 the species as it appears in different localities and at different ages. 

 They also indicate something of the range of variation. 



