JONES : TERRESTRIAL MOIXUSCA IN SOUTH-WESTERN EUROPE. 369 



the specimens, at the same time of year in 1899 it had increased to 

 about twenty-five per cent, of the adults and' even more than that 

 among the young. 



I think an analogy presents itself here between the sudden increase 

 of this variety of Hyalinia ladea and that of var. ellioti of H. coquandi. 

 Both occurred for some unknown reason at the same season of the 

 same year. The specimens of this variety which are found in the 

 Alexandra Gardens and lower parts of the rock generally are as a rule 

 both larger and darker than those obtained at a higher altitude in 

 Gibraltar. 



Var. alba. — Albino-shelled specimens of this species have long 

 been known, but so far as I can ascertain, not yet named. I have, 

 therefore, proposed the above (antea p. 302). Kobelt found albino 

 specimens of H. ladea commonly at Gibraltar, as well as those 

 pseudo-albino forms which usually occur with the animals bearing 

 truly albino shells. At the present time there is one small spot only 

 (so far as I know and I have searched very carefully) where this 

 variety occurs. This place is a slope above the path leading to 

 Monkey-cave range, and is not many yards square. This variety is 

 not very common there and four is the greatest number I have ever 

 taken in an afternoon's collecting. Forms with light fawn or pinkish 

 mouths and often with light yellow translucent bands also occur but 

 very sparingly. 



I also took in the same spot as the albino specimens alluded to above 

 a very curious form in which the five bands were all suppressed except 

 the third one, a condition so common in our own Helix nemoralis, 

 but which, except for my own three specimens, I have never before 

 seen in Helix ladea. 



H. vermiculata Mull. — A few were found among limestone 

 rocks at Aranci Bay, and one specimen in the ancient Roman amphi- 

 theatre at Cagliari in Sardinia. The specimens were all typical. 



H. marmorata (Ferussac). — This is, I believe, the commonest 

 shell-bearing mollusc in Gibraltar, if possible even more so than 

 H. ladea. Everywhere this snail is to be found, even on the walls of 

 the houses in the town and down by the dockyard; but its stronghold 

 is the high slopes on the western face of the Rock, where it can in 

 dry weather be found in the cracks and crevices of the limestone, in 

 masses of twenty or thirty at a time glued together by dried mucus. 

 This is, however, only in dry weather. In wet weather it is very lively, 

 crawling about on the face of the wet rocks and among the herbage. 

 I could not find it at Linea or Algerciras, places in immediate 

 proximity to Gibraltar on the Spanish mainland, although the condi- 

 tions seemed admirably suited to it there. It occurs, however, again 



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