Figure 1. Photographic enlargements of thin sectioned chondrophores from Atlantic surfclams: (a) 139 mm (shell length) age 8; and (b) 137 mm (shell length) age 13. The first annulus formed in the life of a surfclam is sometimes faint (arrow indicates a bold annulus in the chondrophore of the upper clam). The most recent annulus at the marginal edge of these chondrophores was not completely formed.
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