342 American Seashelh 



arks can be placed under the single genus Area. The geological history and 

 morphological studies force us to recognize three subfamilies. Many of the 

 subgenera listed here are considered by some authorities as full genera. 1 

 have refrained from defining their limits. 



Subfamily ARCINAE 

 Genus Area Linne 1758 



Characterized by the long, narrow hinge line with numerous small teeth, 

 by the large byssal notch on the ventral side, and the wide ligamental area 

 between the beaks. 



Area zebra Swainson Turkey Wing 



Plate 2711 



North Carolina to Lesser Antilles. Bermuda. 



2 to 3 inches in length, about twice as long as deep. Color tan with 

 flecks and zebra-stripe markings of reddish brown. Periostracum brown, 

 matted. Ribs of irregular sizes. No concentric riblets. Do not confuse with 

 A. umbonata. A common species which attaches itself to rocks with its 

 byssus. Used extensively in the shellcraft industry. Formerly A. oceiden- 

 talis Philippi. 



Area wnbonata Lamarck Mossy Ark 



Plate 27] 



North Carolina to the West Indies. 



i^ to 2% inches in length. Similar to A. zebra, but differing in having 

 beaded ribs and a very large byssal opening, usually having the posterior end 

 much larger, and in lacking the zebra stripes. Periostracum sometimes quite 

 heavy and foliated. Commonly attached to underside of rocks in shallow 

 water. 



Genus Barbatia Gray 1847 

 Subgenus Barbatia s. str. 



Barbatia eandida Helbling White Bearded Ark 



Plate 271 



North Carolina to Brazil. 



1/4 to 1V2 inches in length; fairly thin, not heavy. Irregular in shape. 

 Byssal opening at base of shell. Numerous weak, slightly beaded ribs; those 

 on the posterior dorsal area being very strongly beaded. Periostracum 

 brown, longest at posterior end. Exterior and interior of shell white. Liga- 





