Handbook of Paleontology 99 



slight current to return the animal to its normal position 

 when overturned. The Scorpion Shell (Pterocera) of 

 tropical seas has a similar winglike extension. This form 

 does not inhabit American waters but is allied to our 

 Wing Conchs (Strombus). 



Effects of varying temperature. Temperature and 

 salinity vary little even at a comparatively small depth in 

 the sea, but along the shore both these factors are impor- 

 tant. In shallow waters, particularly between tide marks, 

 the influence of sun, air and fresh water are felt and 

 there are wide changes both in temperature and salinity 

 of the waters. Temperature in relation to the climatic 

 divisions has been touched upon to a certain extent above. 

 In considering temperature as a factor one must take into 

 consideration both daily and seasonal changes. Animals 

 of the temperate and arctic regions are less affected by 

 wide changes of temperature than animals of the tropical 

 seas, because the variations at the surface in the tropics 

 are slight even between the summer and winter season, 

 so that they are more affected by greater variations when 

 they occur. Temperate and arctic animals can endure 

 excessive cold better than tropical forms can undergo 

 excessive heat. An example has been noted of an occa- 

 sion at Tortugas, Florida, when there were several hot, 

 calm days and the temperature of the shallow water over 

 the Bird Key Reef rose to 92°F-100°F, resulting in the 

 death of many animals such as the octopus, small fish 

 and a number of mollusks over extensive areas. Even 

 the corals were injured. To live through the year in 

 shallow waters, tropical animals apparently must be able 

 to survive a temperature of about 85°F(29°C). Experi- 

 ments suggest that where high temperatures bring about 



