374 JOURNAL OF CONCHOLOGY. 



ABNORMAL SPIRAL BANDING IN OUR LAND AND 



FRESHWATER MOLLUSCA. 



By SYDNEY C. COCKERELL, M.C.S. 



My attention having been called to the occasional appear- 

 ance of spiral lines in some or all of our land and freshwater 

 species, I have recently taken note of every instance which has 

 come under my observation. I append a list : — Bythinia 

 tentaculata, Planorbis coT/iplanatus, P. corneus, Physa hypfwrum, 

 P. fontinalis, LimncRa glutinosa, L. peregra, L. auricularia, L. 

 stg,gnalis, L. palustris, Zonites cellarius, Z. glabet; Z. nitidulus, 

 Z. nittdus, Helix rufescens, If. hispida, H. rotimdata, Bulimus 

 obscuriis and var. albinos, Clausilia rugosa, C. laminata. The 

 lines and bands in question are of an opaque white, often very 

 numerous, sometimes confluent. It is difficult to come to a 

 decision respecting the cause of these bands, but if they be due 

 to reversion, they are less likely to represent original bands now 

 suppressed than the space between such bands or groups of 

 bands. I cannot help thinking that the ordinary colouring in 

 unhanded species is in most, if not all, cases the result of the 

 confluence of an indefinite number of bands originally distinct. 

 If it be true that in all cases of genuine albinisms of species 

 normally banded {e.g., Helix hortensis, H. pisana, H. virgata, 

 &c.), the banded portion alone assumes a translucent aspect, 

 the fact of the albinisms of all our unhanded species being 

 entirely transparent is all in favour of such a supposition ; and 

 the opaque white band on a translucent Bulimus obscurus must 

 represent, if anything, the original ground colour. In some few 

 species, such as both our Physce, Limncea palustris, and notably 

 Planorbis lijtealus, the transformation seems to have been in- 

 complete, an opaque white region at the suture being sometimes 



J.C, iv., October, 1885. 



