STUBBS : ABNORMAL SPECIMENS OF PLANORBIS SPIRORBIS. tOJ 



3. — The apical whorls normal, the last two or three bent down and 

 coiled underneath the shell in corkscrew fashion. 



4. — Shell normal, except the last whorl near the mouth, which is 

 (a), produced at right angles to the shell (in the same plane) ; or (b), 

 bent back and lying flat across the shell ; or (c), bent downwards and 

 coiled right away from the shell. 



5. — Shells twisted into an indescribable tangle. 



6. — Shells flat, but oval, instead of round, with occasional gaps 

 between the whorls. 



7. — Sinistral. Four specimens only have up to the present come 

 into my hands ; three of them are particularly fine (see last three 

 figs., Plate IV.); the other is a young one, but I did not like to run 

 the risk of trying to bring it up to maturity, as the scalariform speci- 

 mens are very fragile. One specimen is a good example of the no. 1 

 form mentioned above, and shows clearly the keel placed on the 

 upper edge of the whorl ; the other is an example of extreme scalarity, 

 the last two or three whorls being entirely disconnected. 1 



By far the commonest form of distortion is for the shell to be nor- 

 mal, with the exception of the last whorl or part of it, which is bent 

 downwards and coiled beneath the shell. 



Roughly speaking, I should say that the proportion of distorted 

 specimens to normal ones in the spot where they are most plentiful, 

 is two per cent. One good sweep of the dredge will bring up about 

 forty or fifty specimens of Platiorbis spirorbis, and there is almost sure 

 to be one monstrosity amongst them ; I once took five in one sweep, 

 but this was exceptional. 



Bullinus hypnorum. — One specimen has the last whorl curi- 

 ously malleated (like Limncea palustris var. lacunosd) and the top 

 whorls turreted. Another has longitudinal lines of growth of a darker 

 colour on the body-whorl, and is much turreted in the top whorls. 

 A third is much turreted, though the body-whorl is normal. 



For comparison with the above three, a specimen of B. hypnorum 

 from another ditch in the neighbourhood is sent. It has an elongated 

 spire, with rounded whorls, an abnormally short body-whorl, and a 

 small mouth. The difference in form between this and the turreted 

 specimens is remarkable, and a novice might be forgiven for thinking 

 them different species. 



Physa fontinalis. — One specimen with a considerably inflated 

 mouth. 



Limnaea palustris. — Several monstrosities in this species have 

 been dredged, the most remarkable being a specimen with a much- 

 expanded mouth, and the lip reflected, as in L. peregra var. labiosa. 



1 Monst. priscum, Taylor, Monogr. Brit. L. F. W. Moll., part 2, p. 117. 



