FISHERY BULLETIN: VOL. 82, NO. 1 



10mm 



5mm 



FIGURE 3.— (a) Left valve of a 15-yr-old ocean quahog, .4rrf<ea islandica, 61.7 mm in shell length recovered on 9 Sep- 

 tember 1980. Estimated 2-yr growth increment was 3.2 mm. The notch-mark area is shown before (b) and after (c) 

 peeling off the periostracum. (d) Optical photomicrograph (microprojector) of five repetitive growth lines in an ace- 

 tate peel of the valve margin. An arrow points to an interruption of growth and growth line formed at or soon after 

 marking the clam. Two additional lines, one midway to the valve tip and one near the valve tip, were formed after 

 marking the quahog. Scale bars of magnification are included. 



FIGURE 4. — (a) Left valve of an ocean quahog. Arctica islandica, 

 about 95 yr old and 91.7 mm in shell length recovered on 9 Septem- 

 ber 1980. Estimated 2-yr growth increment was 0.3 mm. The notch- 

 mark area is shown before (b) and after (c) peeling off the 

 periostracum. (d) Optical photomicrograph (compound micro- 

 scope) of many repetitive growth lines in an acetate peel of the valve 

 margin. An arrow points to an interruption of growth and growth line 

 formed at or soon after marking the clam. Scale bars of magnification 

 are included. 



