128 



The Irish Naturalist. 



July, 



A veiy few words only are necessary to describe the method 

 adopted in the experiments and observations here summarized. 

 With the exception of Lasaea 7-7ibj'a, the only bivalve dealt 

 with, the same tests of vitalitj^ were applied to all the species, 

 whether after exposure to the air in a dry room or after 

 immersion iu fresh water or in water of abnormal salinity. 

 These tests were immersion in ordinary sea water and obser- 

 vation under a low-power dissecting microscope of the first 

 motion of the opening operculum, or observation of the 

 number of individuals out of batches of 5, 10, 15 or 20 

 found resuscitated after a definite period of immersion in sea 

 water. 



The results obtained in the first branch of the inquiry are 

 set out below in the form of a table shewing the maxima of 

 vitality or adaptability to changed conditions observed for the 

 several species dealt with. In this table the periods given 

 for the survival in air of Hj'drobia, Purpura, Lasaea, and 

 Trochus are probabh- close to, and the fresh-water survival 

 periods for H3'drobia and Littoriiia 7ieritoides are probabl}' 

 much under the real maxima. 



Maximum Periods of vSurvivai. of Littorai, MoIvI^usca on {a) ex- 

 posure to dry air {b) initnersiori in fresh water and (c) immersion in 

 water of treble the salinity of sea water. 



In the case of the two species, Lasaea 7-ubra and Hydrohia 

 2dvae, the results above shown are quite unexpected. From 

 its usual habitat, on rocks above high water, where it is 

 frequently exposed to dew and rain, Lasaea might liave been 

 expected to show a large tolerance of fresh water. In no 



