ROPES ET AL.: GROWTH LINES OF OCEAN QUAHOGS 



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FIGURE 9. — Microstructural variation in the shell of ocean quahog, Arctica i.slandica, continued from Figure 8. (Central photograph scale bar = 

 1 jam), (a) Annual growth line sublayer (region between upper and lower-most dark bands) in outer shell layer, located beneath the CA-CL mi- 

 crostructure of Figure 8e. White rectangle encloses the area enlarged in ( b) ( scale bar =10 jam) . (b) The center of the growth line sublayer show- 

 ing FP, SphP, and CompP microstructures (scale bar = 10 jam), (c) Transitional CA-CL microstructure of the growth increment sublayer below 

 (b) (scale bar = 10 jam), (d) ISP forming growth line sublayer within FCCL microstructure. Photomicrograph from area closer to the 

 deposit ional surface than previous photos (scale bar = 1 jam), (e) HOM microstructure interrupted by two prominent ISP bands from a section 

 through the hinge plate (scale bar = 10 jam). 



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