ASHFORD : ON LIMNzEA GLUTINOSA. 7 



escaped his notice, for since I have met with it in the only two 

 locahties which I have searched, and that readily without much 

 loss of time, and have heard from others of its being taken else- 

 where, it is only fair to presume that glutinosa has an extended 

 and perhaps general distribution in that island. It is extremely 

 desirable to have every possible information respecting this species 

 that the question may be settled whether there is specific or only 

 varietal distinction between it and Z. involuta. My own opinion 

 is ih.zX L. glutinosa has broad and persistent characteristics both in 

 shell and animal separating it decisively from Z. peregra, and that 

 Z, involuta is merely a well marked variety of Z. glutinosa, due 

 to continued peculiarity of surroundings producing a cumulative 

 effect upon successive generations. Their animal parts are allowed 

 to be alike, they are both said to exhibit a reflected mantle 

 (peculiar to themselves), and their shells do not differ to any- 

 thing approaching the same extent as those of the typical 

 Z. peregra and some of its admitted varieties. I have carefully 

 looked over my thirty-six specimens from King's co., and detect 

 among them not only a shght difference in the extortion of 

 the spire, but also in the proportions of the aperture; and Mr. 

 Jeffreys records specimens received by him "in which the spire is 

 more or less intorted, resembling in this respect the form of Z. 

 involuta.''^ Surely less powerful agencies may be supposed neces- 

 sary to have effected the comparatively slight divergence of shape 

 in the shells of these two forms than those which have transformed 

 the ordinary Z. peregra into the dwarfed and solid Z. viaritima 

 with its produced spire on the one hand, and into the thin, 

 ampullaceous Z. ovata on the other. It is a fact too of some 

 little relevancy to the question at issue, that those varieties of Z. 

 peregra which deviate from the typical form in the same direction, 

 so to speak, as Z. involuta deviates from Z. glutinosa, viz. : — Z. 

 lacustris and Z. Burnetii frequent habitats of a character similar to 

 that in which Z. involuta has been found. Discussion, however, 



