The Nautilus. 



Vol. VI. OCTOBER, 1892. No. 6 



ON THE AMNICOLOID GENUS LYOGYEUS, WITH THE DESCRIPTION OF 

 A NEW SPECIES. 



BY HENRY A. PILSBRY. 



Some years ago the writer had occasion to examine the dentition 

 of the type species of Gill's genus Lyogyrus^, and to show that it is 

 not allied to Valvata as supposed by all earlier systematists, as well 

 as by Tryon^ and by Fischer^ ; but that it is undoubtedly a mem- 

 ber of the family Amnieolidoe. (Hydrobiidae of Fischer), and in 

 fact, is not far removed from the genus Amnicola. The same 

 results have been independently obtained and fully confirmed by 

 Mr. Charles E. Beecher* whose preparations and unpublished draw- 

 ings of the radula of Lyogyrus pupoides show conclusively the true 

 systematic position of this interesting genus. 



Lyogyrus may be shortly described as a fresh-water Rissoid hav- 

 ing the shell of Amnicola', the operculum of Valvata and the denti- 



^ Pilsbry, in the Conchologists Exchange, vol. ii, p 113, 1888. 



^ Structural and Systematic Conchology, vol. ii, p. 274, 1883. 



^ Manuel de Conchyliologie, p. 735, 1885. 



* Beecher in MS. et litt. 



^ In some localities L. ptipoides has the entire latter half of the body whorl 

 free from the preceding whorl : but in the great majority of specimens this char- 

 acter is less marked than in the form originally described by Gould ; and very 

 often the peristome is actually in contact with the body-whorl for a short dis- 

 tance, as in a normal Valvata. The original V. pupoidea is an exaggerated and 

 extreme phase of a species varying much in degree of compactness. It is there- 

 fore obvious that the character of having the last whorl free from the preceding 

 whorl is not a generic or even a constant specific characteristic. 



