Quarterly Journal of Conchology. 173 



applied, with others, as an assistant in determining a species, but it 

 is not absolute, nor is any rule which can be laid down. I have tried 

 to explain the grounds upon which Dr. Jeffreys has proceeded in 

 joining H. nenwralis and H. hortensis together, but I must here 

 record my belief in their distinctness. 



Mr. Simpson asks — ^•^Qd^xxvgoi Helix }iortensis—\iO\v is it that the 

 variety becomes permanent? Do not all shells (moUusks?) follow the 

 samq laws as other animals in returning back to the original, or in 

 throwing off other varieties which differ from the variety itself as 

 much as it differs from the typical species?" Now " varieties are of 

 twokinds — permanent and /i3fa/"— the former are distributed through- 

 out the country, the latter are confined to one spot or district ; as 

 ''■permanent''' forms we may quote Ifnio tumidusvM:. radiata, Ano- 

 donta anatina var. ventricosa, Limntea peregra var. intermedia, and 

 Helix caperata var. ornata ; as " local " we may take Unio pictorum 

 var. compressa, Anodonta anatina var. complanata, Limncea peregra 

 var. picta, and Helix virgata var. carinata. 



There is abundant evidence to shew that some species of mollusks 

 are more subject to variation than others, as among the higher 

 animals, and it is this tendency to vary which would make "con- 

 fusion more confounded" by attempting to name varieties. 



I must confess I am surprised at Mr. Simpson finding specimens 

 oi Helix rufescens and H. hispida "exactly alike" and should like 

 to see examples. It seems to me, that the hispid epidermis — at all 

 stages of its growth — of the latter and its smaller size (excluding 

 all other characters) form prominent features of distinction not to 

 be mistaken. 



As to whether the separation of Helix concinna and H hispida 

 is "too critical" or not, I must say that I think it is. 



The differences between Clausilia biplicata and C. laminata are 

 decisive — -no such distinctive characters obtain with the vars. of 

 Carychium minimum. Again, the difference between Cochlicopa tri- 

 dens and C. lubrica cannot possibly be considered as "slight" as 

 thatbetween the variations of C. minimum. The lattervaries, itistrue, 

 but the same general character runs through all the variations, and 

 they are all so intimately blended that it would be useless to attempt 

 to name any of them, I have examined numbers of the American 



