I 14 J. D. HAM-MAN. 



ponds. Ii is always more abundant along protected ci >a-t- and 

 hence its absence I'niin Nobska Point, which i- exposed to the 

 open -c-a, was to be expected. 



1 Individual- ot Litorina li!on-a i -aid to have been imported 

 to tin- American coast from Europe) usually live on rock) -nrfaces 

 \\ Inch lie bet \\i-en the high-lide mark and one loot below the lo\\ - 

 lide mark. The specie- \\a- not loiind in 1 a-hmo I'oiid but a 

 l'e\\ \oung individuals \\ere -ecu in ('.rape Pond living ( ii trau-- 

 plauted oysters. This observation, taken in connection with 

 other- described belou , indicates that the absence ol Litorina from 

 these bracki-h pond- \\.i- not due, direct ly. to the lower specific 

 gl avity that t'xists there. 



In order to explain the restricted distribution of Litorinn the 

 following obserxations and experiments \\ere made: 



A. l-'ood.- Litorina fxillid/u is neail\ a!\\a\s found on two 

 t I'ininon species of rock weeds, and its supply of food is doubt- 

 less associated with these plants, while Litorina rudis and 

 litorea eat small green al^a- which grow more abundantly on 

 the rocks which are situated between the tidal marks. 



When individual- of Litorina litorea were placed in shallow 

 aquaria, which contained rocks from the sea shore, from Lagoon 

 Pond or from the street and contained also pieces of glass and fish 

 they came to nest for the most part on the rocks taken from 

 normal sea water. The snails, which were taken from the 

 entrance to Lagoon Pond with their accompanying rocks, a!-o 

 -ettled on the sea rocks. 



B. Salinity. When indi\ iduals of Litorina litorca were placed 

 in a mixture of equal part- of fresh and sea water, they were 

 able to crawl about; but when they were placed into a mix- 

 lure of two parts fresh and one part sea \\ater, all died within 

 ei-ht days. When the\ \\ere placed in sea water, to which a- 

 much as fourteen grams of sun e\aporated sea -all had been 

 added to each Xoo c.c. of sea water, all died within eight da\-. 

 The specific gra\ityof the various u-st solutions indicated that 

 Litorina could li\e in water which has a louer specific gra\ii\ 



t han was obsei \ ed in < .rape and T.ishmo ponds. 



('. '/'<-nif><-rali<r<-. -The \aiiation in the tempera! tire along the 



coast did not appeal t,itlect the distribution ol Litorina. Snails 



