These regression equations, each of which repre- 

 sented growth for a different time interval, were 

 then transformed to a common, 52-week, time 

 interval using Lindner's (1953) method. 



Taking an average slope and intercept gives 

 Z (+1 = 47.3 + 0.662 L, (equation 2) as the estimate 

 of growth per year by this method. 



Figure 9.— Upper valve showing the result of heavy invasion of boring organisms. The annual rings 

 are located between the areas of heaviest damage. 



306 



U.S. FISH AND WILDLIFE SERVICE 



