416 FOSSIL OSTREID^ OF NORTH AMERICA. 



PLATE LXXV. 



Fig. 1. — Young American oyster, viewed from the side immediately after fixation by 



the mantle border hi ; enlarged 183 times. 

 2. — Four young European oysters taken from the beard of the parent ; enlarged 



96 times. 

 3. — ^YouDg American oyster, with the beaks or umbos of the larval shell devel-- 



oped, and firmly attached to au old oyster-shell ; enlarged 96 times. 

 4. — Young American oyster, attached and beginning to form the spat shell. (The 



valves are slightly displaced.) Enlarged 96 times. 

 5,6. — Very young spat of the American oyster, showing the jjeculiar form of the 



true larval shell and that of the spat, and the upwardly directed hinge 



border ; enlarged 35 times. 

 7. — Lower valve of very youug oyster, showing the great concavity of the larval 



valve and the abrupt transition into that of the spat stage; enlarged 35 



times. 

 8. — Older spat viewed from the lower surface after being detached ; enlarged 35 



times. 

 9. — The same specimen viewed edgewise, to show the flat lower valve of the spat 



and the convex upper one, and the upturned hinge with the larval valves 



iu place ; enlarged 35 times. 



N. B. — Figures 3, 4, 5, 6, 7 and 8 are unfortunately reversed, owing to au oversight 

 in transferring the original camera lucida sketches. The peaks of the umbos should 

 look to the left instead of to the right in order to bring them into a natural position. 

 Otherwise these figures are accurate. 



