64 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 54. 



Though the annual mean gives a ready basis for comparison, and 

 furnishes an index of general chmatic conditions, it is probably not of 

 itself as effective in determining distribution of aquatic animals as 



Fig. 4.— Isotherm map of the world, with the isotherms of Corona and Frances drawn in. 



other peculiarities of temperature, such as maximum and minimum 

 temperature at certain seasons. Figure 6, a graphic representa- 

 tion of mean monthly minima for the three stations, shows that at 



Fig. 5.— Mean temperature by months. 



Corona there are six months in the year during which zero F. is 

 commonly reached, and that further, during all months, freezing tem- 

 peratures may be expected. As a matter of observation, frosts are not 

 uncommon during the entire summer in the higher parts of this region. 



