12 VIVIPARA. 



since been used as genera by Mr. W. G. Binney 

 in his recent monograph published by the 

 Smithsonian Institution. I prefer to continue 

 to regard these groups as subgenera, because 

 some of the characters of the soft parts de- 

 scribed by Mr. Binney are of very doubtful 

 distinctive value in my estimation. I may 

 particularly adduce the descriptions of the 

 animals of Vwipara and Melanilio. 



"^Vivipara. Foot of moderate size, thick, 

 not produced beyond the snout. Colors very 

 dark." Fig. 23, Binney s Viviparidce. 



''Melantho. Foot large, rather thin, broad, 

 much produced beyond the snout. Colors 

 rather light," etc. Fig. 68, same work. 



Now either description will apply to either 

 genus. When the animal is at rest description 

 No. 1 will apply, but when it walks it becomes 

 No. 2. Thus Sixysdecisa belongs to the genus 

 Vivipara when quiescent, but has the remark- 

 able faculty of walking and reaching into the 

 genus Melantho ! 



Those who are curious about this matter, 



[38] 



