326 
ZOOLOGY: W. J. CROZIER 
less abundant on the south shore, but there are also relatively more of the 
chitons requiring it; at Long Island more shelter is afforded, in crevices, from 
the sun's heat at intertidal periods; at Cross Bay the older chitons, which live 
/ Z & f> * 6 7 8 $ to 7? f& 
FIG. 1. THE RELATIVE GROWTH OF CHITON TUBERCULATUS IN DIFFERENT ENVIRONMENTS 
O Long Island, Great Sound (422 individuals). X Grace's Island, 
Great Sound (81 individuals). 1 Cross Bay, South Shore (591 individuals). 
FIG. 2. THE PERCENTAGE SURVIVAL OF CHITONS ATTAINING THE AGE AT WHICH DYING- 
OFF BEGINS 
• - Great Sound (515 individuals); O = Cross Bay, south shore (396 individuals). 
further down the beach than do the younger ones, 2 are frequently covered to 
a depth of a foot or more by sand washed up by the tidal surf, and especially 
at times of southerly storms. The cooperation of these several differential 
