42 Land and Freshwater Mollusks. 



anatomical curiosity now without further detail, merely to call 

 attention to the necessity of at least a rapid examination of the 

 most frequently recurring specimens, if we would not lose objects of 

 curious interest. Again, this species of Clausilia has afforded the 

 only reversed specimen of that genus \Yhich I have seen in this 

 country ; as the typical form of the genus is sinistral, the reversed 

 shell is dextral. This interesting and very rare variation from 

 ordinary structure was found by a young collector in Kent. 

 Another genus which sometimes yields specimens departing from 

 the ordinary type is Planorbis ; this is a freshwater tribe of shells, 

 mostly disk-shaped, flat, and thin, coiled like a cable on the deck 

 of a ship ; of these Planorbis carinatus and marginatus are occa- 

 sionally found with their coils as it were lifted up, and thus, instead 

 of the depressed discoid form, a sort of partially open spiral is 

 produced. This opening of the coils of the spire also occurs in 

 some helices; in England the common Helix aspersa is occa- 

 sionally so found ; on the cover of Gray's edition of Turton's 

 Manual, an illustration of one of these curious specimens is given. 

 There are examples, I think, in the British Museum. One of the 

 Liumsei, a freshwater tribe, sometimes shows a curious development 

 of the shell ; this is Liranseus auricularius, which has a broadly 

 expanded lip ; this expansion is exaggerated sometimes to a 

 singular degree, and I have specimens where the lip is turned over 

 and folded on itself, so that the animal one would suppose must 

 have been curiously confined and embarrassed in movement ; these 

 I found in the Maes in Holland. 



Besides variations of structure, there are interesting and still 

 more frequent variations of colour ; of some shells whose ordinary 

 colour is dark brown, beautiful semi-transparent white specimens 

 occasionally occur ; shells, in fact, whose inhabitants seem to have 

 no power of secreting the colouring matter, cOmmonly characteristic 

 of their species. I have found such specimens of Clausilia biplicata 

 (also called bidens), Bulimus obscurus, Zua lubrica, Azeca 

 tridens (this very rarely) and several of the small helices : these 

 colourless shells should be examined with the animal alive, that 

 the collector may not at first mistake a faded shell for a white 

 variety. As a contrast to this absence of colour, may be noticed 

 a variety which occurs occasionally of Helix ericetorum — this is a 

 flattened shell living on downs and exposed localities, commonly 

 white with brown bands mote or less distinct — but it is sometimes 

 found wholly of a greyish brown, the bands showing of a lighter 

 tone. The banded snail, Hehx virgata, is most various in colour, 

 but the varieties do not appear capricious ; they can be grouped or 

 classed, and here accurate observation is needed, more having been 

 done in this direction abroad than has yet been attempted in 



