22 THE NAUTILUS. 



iation and whether this variation increases with wear and age. 

 Biometric studies upon hundreds of radulae would be of great 

 service. A variable radula renders tooth formulas of little value 

 as has been stated by Roszkowski. In the American species 

 examined this variability has been of such small percentage as to 

 cause little or no difficulty in placing species in their appro- 

 priate groups. 



The genitalia seem to provide characters of greater stability 

 than do the radulae. The genitalia of the European and Amer- 

 ican species agree in all essential details and it seems true that 

 these organs offer characters sufficiently stable for the separation 

 of groups of species as has already been done in the writer's 

 monograph of this family. Some years ago the opinion was 

 expressed in a letter to Roszkowski, that the short, pyriform 

 receptaclum seminis without long canal which is found in ovata 

 Drap and profimda Clessin would seem to provide a character 

 of group importance (see Roszkowski, plate 17, figs. 196-197). 

 The length of the epiphallus allies these species with auricularia 

 in the genus Radix. The writer hesitates to add another name 

 to this already overburdened family, and simply suggests that 

 this character may be found of value in a future classification 

 should it occur in other species. This form of receptaculum 

 seminis has not been observed in any American species of Lym- 

 naea. Roszkowski' s paper is a valuable contribution to our 

 knowledge of the Lymnaeas and similar studies on other species 

 (American as well as European) would greatly aid in providing 

 reliable data for a satisfactory classification of this family. We 

 wish that some American post-graduate student would elect 

 such a theme for his doctorate dissertation. 



In a recent paper, 1 Mr. Harold S. Colton publishes some 

 valuable suggestions on the classification of the Lymnseids. 

 While the writer would not for a moment claim that he has 

 said the last word on the classification of this family, he does 

 not believe that anything would be gained by a return to the 

 old use of the name Lymnaa. While the differences proposed 

 for the separation of the names admitted to generic rank in the 



1 NAUTILUS XXVIII, pages 116-120, Feb., 1915. 



