GASTEROPODA OF THE UNITED STATES. 



53 



reous humor ; but the character of the retina I did not 

 detect at the time. Whether a crystalhne lens exists or 

 not I am in doubt ; at the time of making the investiga- 

 tions, in several instances I thought I discerned it very 

 distinctly ; but in other instances, even when larger spe- 

 cies were examined, if it existed it escaped mj observa- 

 tion. 



