BIVALVES CHAM A. 49 



CHAMA Clamp, Clam, or Gaper. 



DESCRIPTION OF PLATE XII. 



DiT. L—fam. 1. Fig. 1. C. gigas. Fanu 3. Fig. 6. C. concamerata. 



Fam. 1. Fig. 2. C. hippopus. Fanu 6. Fig. 3. C. cor. 



Fam. 2. Fig. 4. C. antiquata. DiT.II.— Fig. 7- C. gryphoides. 

 Fam, 2. Fig. 5. C. rosea. Fig. 8. C. arcinella. 



Shell bivalve, rather coarse; hinge with a callous gibbosity, oblique' 

 ly inserted in an inclined hollow ; anterior slope closed. 



THIS genus contains only twenty-seven species, but 

 presents considerable diversity in character. It com- 

 prehends species the most dissimilar in form and mag- 

 nitude, and some as remarkable for their symmetry as 

 others are for their deformity. 



It would be difficult, with the exception of the cal- 

 lous gibbosity of the hinge, to point out a distinction 

 by which the shells of this genus might be recognised. 

 The forms it exhibits are the suborbicular, reniform, 

 cordate, and rhombic. The posterior slope gapes only 

 in the C. gigas and C. hippopus, (and not always in 

 the latter), but the anterior is universally closed, and 

 the margin crenulated. Almost all the species are 

 equivalve, and many of them are inequilateral. The 

 exterior is usually ribbed or striated longitudinally ; it 

 is also scaly, or tuberculated ; some specimens are 

 richly foliated or spined ; and others are nearly smooth. 

 There are two formations of the Chama which deserve 

 particular notice, viz. the cordiform and concamerated. 

 The first is exhibited in the C. moltkiana and C. cor, which 

 E 



