FAMILY 10. ARCACEA. 107 



be relied upon as a generic character. The presence of a byssus is pe- 

 culiar to some of the Mya and one or two other genera ; we therefore 

 cannot appreciate the genus Byssoarca of Swainson. 



The shell of Area may be described as being equivalve or nearly so, 

 inequilateral, and more or less ventricose ; it is often covered with a hairy 

 or fibrous epidermis ; and the umbones are distant, receding from each 

 other by the increase of the area between them. The hinge is linear, 

 straight, consisting of a series of numerous small teeth. The ligament 

 is externa], attached to the area between the umbones. The Areas are 

 sometimes provided with a byssus. 



Examples. 



PL LXXXII. Fig. 1 . 



Arca NoiE, Linnaeus, Syst. Nat., p. 1140. Lamarck, Anim. sans vert., 



new edit., vol. vi. p. 4G1. Enc. Meth., pi. 303. f. 1. a, b, c. 

 Byssoarca Noa, Swainson. 



PI. LXXXII. Fig. 2. 



Arca granosa, Linnaeus, Syst. Nat., p. 1142. Lamarck, Anim. sans 

 vert., new edit., vol. vi. p. 471. Enc. Meth., pi. 307. f. \. a, b. 



PL LXXXII. Fig. 3. 



Arca in^equivalvis, Bruguiere, Diet., No. 16. Lamarck, Anim. sans 



vert., new edit., vol. vi. p. 472. Enc. Meth., pi. 305. f. 3. b. 

 Arca Indica, var., Dillwyn. 



PECTUNCULUS, Lamarck. 



Testa orbicularis, sublenticularis, sequivalvis, subsequilateralis, epidermide 



pilosa saepe induta ; umbonibus pariim separatis, area intermedia par- 



va ; marginibus valvarum plerumque crenulatis. Cardo arcuatus, 



p2 



