MOLLUSC A 155 



The shells of Venus mercenaria as well as V. 

 campechiensis from the Pleistocene are often consider- 

 ably thicker than those living' today. 



Venus mercenaria notata Say 



A variety of the common clam (V. mercenaria) 

 with zig-zag' color markings on the shell ; said to live 

 on the sandbars off shore; shells are occasionally 

 found on the beach, but the variety is by no means 

 common. 



Venus campechiensis Gmelin 

 (T\ morioni Conrad) 



Very similar to V. mercenaria but distinguished 

 from it by having its concentric ridges extending 

 across the entire shell, whereas in mercenaria they are 

 obscured except near the beak. Campechiensis never 

 has the interior purple characteristic of mercenaria. 



V. campechiensis is a southern form and in the 

 Carolinas, Georgia and Florida may attain a con- 

 siderable size (as much as 8 inches in diameter). 



New Jersey specimens arc very small — rarely 

 more than 2 inches in length — and can usually be 

 distinguished from mercenama by their conspicuous 

 concentric ridges. 



Gemma gemma Totten „ (Gem Shell) 



A minute clam (usually less than ] 4 inch) with 

 typical venerid hinge, frequently found in great 

 numbers in tide pools along the entire Xew Jersey 



