PLATE V. 



Fig. 7. Young oyster from the side of a vessel in Provincetown, Mas- 

 sachusetts, showing five silphologic stages of growth of the right valve 

 (Is, 2s, 3s, 4s, 5s). The first two stages were drawn from a younger spec- 

 imen as they were worn off in the specimen in hand. Life size. 



Fig. 8. Young oyster viewed from the hinge end. p, Prodissoconch ; 

 Iv, Left valve; rv, Right valve; s, Early spat growth. The left valve has 

 not yet flattened to the object of attachment. 



Fig. 9. Tip of left valve of an oyster from inside whorls of a dead 

 Busycon, where it was preserved from all eroding action, p, Prodisso- 

 conch; s, Spat growth; Z, Ligamental groove;/, Flange-like extension 

 of margin of the shell over the object of fixation ; b, Border of shell 

 proper, exclusive of flange. Magnified seventy-five times. 



Fig. 10. Young oyster growing on glass, viewed from right side, show- 

 ing p, Left and right valves of prodissoconch ; Is, First silphologic stage. 



Fig. 11. Same specimen as fig. 10, viewed from left side through the 

 glass on which it was attached, p, Left valve of prodissoconch; Is, First 

 silphologic stage. Figs. 10 and 11 magnified thirty-six times. 

 (552) 



