Handbook of Paleontology 107 



waters is most marked in the neighborhood of small bays 

 or estuaries and there are certain seasons when the influ- 

 ence is greater. The invariable presence of the green 

 seaweed, Enteromorpha, along shores is a witness to the 

 fact that there is hardly a patch of the rocky foreshore 

 which does not receive its share of fresh water, for other- 

 wise it would not thrive. Even the life of the shore pools 

 does not escape. Conditions of life here are affected by 

 the same phenomena that cause variability in the tempera- 

 ture and salinity of the coastal waters. Heavy rains 

 freshen the waters of the pools, and under the influence 

 of a strong sun evaporation increases their salinity. The 

 salinity of rock pools has been found to vary anywhere 

 from a little above two or three grams of dissolved salt 

 to about a quart of water to over 300 grams of salt per 

 quart. Such pools are inhabited by protozoans and small 

 crustaceans in large numbers. Studies of certain of the 

 flagellate protozoans of shore pobls show that under the 

 most favorable conditions they may be present in such 

 numbers as to color the surface of the pool green. If 

 the water evaporates until it is strongly saline these small 

 organisms come to rest, showing no signs of life. This 

 is known as a period of latent life and they remain in 

 this state until the condition of the water again becomes 

 suitable, which may be even for two or three weeks. The 

 little crustaceans (Copepods) may also have to contend 

 with severe conditions, since in wet weather the pools 

 may be flooded and in a dry summer may be even com- 

 pletely dried up. The green seaweed which covers pools 

 above high-water mark is a shelter and refuge for enor- 

 mous quantities of these small forms. They thrive best 

 in the pools when the water in the pools is fresher and 

 experiments with some of them have shown that both 



