36 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 2 



no clue to its identity. It is suggested that a fish may have been 

 responsible for the damage. 



4. The direction of costal divergence is taken as the direction of 

 progressive shell growth in the regenerated area. The precise mode 

 by w^hich the shell was rebuilt is obscure. 



5. Regenerative growth was sufficiently rapid to complete the 

 "patch" before fatal damage was done to the exposed animal. 



6. The injury probably occurred when the shell had very nearly 

 reached its present size, or at least had reached the first growth 

 undulation posterior to the margin. 



