Arcidae 35 



Art-a umboiiatai'' Lamarck PI. 2, fig. 10 



Alt., 30; length, 64; diam., 34 mm. Dull white, concentric-shaded 

 markings of brown; shaggy epidermis, heaviest behind; shell not 

 thick and somewhat translucent; equivalve; inequilateral, sharply 

 carinate posteriorly; umbos prominent, recurved, widely apart; 

 hinge margm straight with a little upward curve at posterior end; 

 anterior and posterior margins sinuous, ventral margin rounded with 

 byssal notch below umbos; six to eight definite ribs on the posterior 

 keel, remainder of surface finely and rather irregularly cross-ribbed 

 by growth lines; typical comb-toothed hinge; margins and internal 

 surface of valves smooth, dull purple; muscle scars and pallial line 

 typical; shells often covered with a growth of sponge. 



From three to seven fathoms. 



Genus ANADARA Gray, 1847 



Subgenus SCAPHARCA Gray, 1847 



Anadara notabilis^'' (Roding) {A. auriculata Lam.) PI. 1, figs, 6a, b 



Alt., 40-45; length, 60-65; diam., 35-40 mm. Altitude and 

 diameter great in proportion to length. Shell thick, heavy, dirty 

 white with an abundant silky, brown epidermis; equivalve; in- 

 equilateral, longest posteriorly; umbos well apart, recurved and 

 directed forward; hinge area widest directly in front of umbos. About 

 28 rounded ribs with cross sculpture of fine, elevated ridges — almost 

 obsolete in intercostal spaces; the five or six anterior ribs have a cen- 

 tral longitudinal furrow; hinge margin straight, ventral and anterior 

 margins rounded, posterior margin sinuous; fine comblike teeth; 

 interior of valves smooth, white, sometimes pink-tinted in umbonal 

 region; inner margin with deep indentations corresponding to ribs 

 and Interspaces; well-impressed muscle scars and pallial line. A short, 

 thin, dark-green byssus composed of narrow flat strands expanded 

 in fan shape at distal end to several times its width at byssal notch. 

 In the young mollusk the byssus consists of only a few threads. 



Dredged in three to six fathoms. 



^5 Lat., umbo, beak, tip. 



^^ Lat., notabilis, noteworthy. 



