I9IO- CoLGAN. — The Adaptability of Littoral Mollusca. 127 



NOTES ON THE ADAPTABIIvITY OF CERTAIN 

 LITTORAL MOLLUSCA. 



BY NATHANIEI. COLGAN, M.R.I.A. 



There is perhaps hardly any fact in the economy of our 

 marine mollusca more trite and obvious even to the unscientific 

 observer than the capacity possessed by many of our common 

 littoral species of enduring long periods of exposure to the 

 air. Yet, so far as I am aware, no attempt has been made to 

 determine the comparative capacity in this respect of the 

 various species, much less to ascertain whether in any given 

 species the capacity is equally shared amongst all its members. 

 The field of research in this direction is, in faci, so imper- 

 fectly explored that the results here given of some simple 

 experiments and observations recently carried out by the 

 writer of these notes are not unlikely to offer something 

 new. 



The material dealt with was all collected on the shores of 

 Co. Dublin during the three months from the middle of 

 October of last year to the middle of January of this year, and 

 was made up of 7 operculate univalves, Hydrobia ulvae, Lit- 

 torina 7ieritoidcs, L. riidis, L. littorea, L. obttcsata, Purpura 

 lapilhis and Trochus U7nbilicatus, with one bivalve, Lasaea 

 rubra, or a total of 8 distinctly littoral species. The inquiry 

 was directed to the following points : — {a) the length of time 

 which each species was capable of living when removed from 

 the water and exposed to the air in a dry room ; whether, and 

 if so, for how long, any of them could survive immersion ijj) 

 in perfectly fresh (non-saline) water, or {c) in water of abnormal 

 salinity — i.e., a salinity three times that of ordinary sea water. 

 In the case of two of the species. Purpura lapillus and Litto- 

 ri7ia mdis, an attempt was also made to determine whether 

 there was an}' marked difference in the vitality or adaptability 

 shown by individuals taken from stations at or above high- 

 water mark, as compared with others of the same species taken 

 at low water or between tide marks. 



