ADAMS : ON SOME BRITISH LAND AND FRESHWATER SHELLS. 299 



indeed are exposed, unless they are white, like the tentacles them- 

 selves. These, indeed, are terminated by a convex surface, very 

 smooth, very shiny, surrounded by a slightly-impressed ring ; which 

 surface doubtless answers to the eye of other terrestrial molluscs. But 

 this animal, probably because it lives underground, where it cannot 

 use eyes, appears to us plainly to lack eyes." Now I have noticed 

 that these peculiar convex endings with a constricting ring are in fact 

 eyeballs, and also that they are retractile, but whether they have 

 retained the power of sight in spite of their loss of pigment, I am not 

 prepared to say (see fig. 2b). As far as my observation goes, the 

 animal is insensible to light, though it will crawl straight away to a 

 heap of moss ; the direction, however, may be determined by scent 

 alone. If it is deficient in sight it certainly uses its tentacles to all 

 appearance in the same manner as its more favoured brethren. I may 

 mention in this connection that an albino specimen of Limax maxzmus, 

 whose eyeballs were also destitute of pigment, seemed to act in a perfectly 

 normal manner. Though my observations on this point (J. Conch., 

 vol. 9, p. 24) tend to shew that this species is lacking in sight, I am not 

 aware to what degree of perfection the vision of terrestrial mollusks 

 attains, but I have noticed that Cyclostoma elegans and Helix pomatia 

 seem sensitive to the approach of a large object. 



Limn^a burnetti Alder and L. involuta Thompson. — There 

 has always been much doubt as to whether Z. burnetii and Z. invo- 

 luta are worthy of specific rank, or whether they are by-forms of 

 Z. peregra, and so far the authorities have been in favour of according 

 specific rank to Z. involuta, and withholding it from Z. burnetti. 



A year ago (September ioth, 

 1898) my friend Mr. A. G. Stubbs 

 and I paid a visit to Z. involuta in 

 its native tarn, and had the oppor- 

 tunity of observing the animal in 

 its very young stage. The little 

 creature, less than two mm. in alti- 

 tude, showed a decided spire 

 (fig. 3A) exactly like that of a 

 young Z. peregra, but individuals 

 B very slightly more grown showed 



FK, 3. Youn^ g s^ofZ«.. ^ ^^ grQwn up ^^ ^ 



B . l. bumetti. spire which was sunk below the 



ridge of the whorls. Now, a very interesting photograph, taken by 

 Mr. J. Madison, of Z. burnetti one day old and not quite a millimetre 

 in altitude, shews the spire clearly intorted— more so indeed than is 

 the case with the adult shell (fig. 3B). 



