Arcidae 37 



From two to five fathoms. 



Genus BARBATIA Gray, 1842 

 Barbatia tenerai^ (C. B. Adams) PI. 40, fig. 288 



Alt., 25; length, 35; diam., 15 mm. White, translucent, a soft 

 shaggy, brown epidermis covers the shell except over the umbos and 

 is heaviest posteriorly; equivalve; nearly equilateral; umbos high, 

 near together and strongly recurved; hinge area narrow, flat, ill de- 

 fined; hinge margin almost straight; anterior and ventral margins 

 rounded, posterior margin strongly curved outward; sculpture of 

 numerous fine, close ribs, stronger posteriorly, all crossed by growth 

 lines; hinge typical but not strong; interior smooth, white, finely 

 lined; margins smooth; pallial line and muscular scars present. Speci- 

 mens from the Gulf of Mexico are somewhat smaller and thinner 

 than Atlantic individuals. 



Dredged at two fathoms. 



Subgenus ACAR Gray, 1857 

 Barbatia rtomiiig'ensis (Lamarck) (.■?. reticulata Gmelin) PI. 3, fig. 11 



Alt., 7; length, 20; diam., 10 mm. White, fairly thick, with 

 thin, light-colored epidermis; equivalve; inequilateral, keeled at 

 posterior end; umbos recurved and closely approximate; hinge area 

 small, margin straight; ventral margin slightly curved with byssal 

 notch below umbos; anterior margin curved, posterior margin 

 strongly curved at junction with ventral margin; reticular sculpture 

 of radiating ribs crossed by stronger, concentric, almost lamellar 

 growth lines; interior white, smooth, margins finely crenate; muscle 

 scars and pallial line well defined; byssus comparatively large, thick 

 and flattened. 



Taken about reefs. 



Genus ARCOPSIS von Koenen, 1885 

 Arcopsis adamsi conradiana (Dall) PI- 3, fig. 12 



Alt., 7; length, 12; diam., 5.5 mm. Shell white, sometimes brown- 

 ie Lat., tenera, delicate. 



