176 PROCEEDINGS OF THE ACADEMY OF [May,. 



varieties of Lymncea from one another, and what is the character of 

 the variation within one species? 



The most recent work on the systematic relationships of the 

 various species and varieties of Lymncea is the monograph on the 

 group by F. C. Baker (1911). This writer recognizes one hundred 

 and two recent species and varieties which he distributes through 

 six genera as follows: Lymncea, two species and three varieties; 

 Radix, one species; Bulimncea, one species; Acella. one species; 

 Galba, fifty-eight species and twenty-eight varieties. The characters 

 on which these genera are distinguished from one another are as 

 follows : the relative size of portions of the male reproductive organs, 

 whether there are one or two penis sac retractors; whether there 

 are two or three cusps on the lateral teeth; proportions of the jaws, 

 length of the spire, axis of the shell gyrate or not, sculpture of the 

 surface, etc. It will be noticed that all these characters, with the 

 exception of two, are purely quantitative. The character of the teeth 

 is a qualitative difference to which the author attributed little 

 importance, as his Galba obrussa has the same type of radula as his 

 Pseudosuccinea columella when the latter is half-grown. There is 

 no qualitative difference between the radulse of the adults. Many 

 Galba have tri- and other Galba have bi-cuspid lateral teeth. Of 

 the one hundred and two species and varieties, of but thirty-two did 

 the writer know aught of the anatomy of the reproductive organs. 

 Nothing is apparently known of the internal anatomy of the type 

 species of the genus Galba, that is, Galba tnmcahda Muller. Since the 

 important characters in describing the genera are purely quantitative, 

 the present writer feels that he cannot accept these genera and will 

 for the present consider the old genus Lymncea as including them all. 

 When we know more, some genera may, perhaps, be farther separated. 

 Not being a systematist, the author cannot criticise this work and he 

 is very thankful that someone has taken the trouble to examine all 

 the literature and the species of this interesting group, bringing it 

 together in one work. 



The individual species are separated one from the other by quanti- 

 tative differences in the shell characters, body characters, by color, 

 and where known the genital organs, the radula, and jaw. This 

 roughly outlines the sort of variation that takes place within the 

 genus. Within a single species what can we look for? 



In the present case, where selection is hoped to be practiced, 

 characters visible on the exterior can alone be considered. This 

 forbids us at the outset dealing with any characters of the internal 



