264 B. H. GRAVE. 



EXPLANATION OF PLATE I. 



FIG. I. Shows the left valve as it appears from surface view. It is not quite 

 symmetrical. 



FIG. 2. Shows the right valve as it appears from surface view. The prominent 

 notch at the base of the anterior ear can be seen. 



FlG. 3. Is a view of the inner surface of the right valve. The dotted line shows 

 the position of the cartilage pad which aids in opening the valves. 



