Cfi-nnostren.] PELECYPODA. 1033 



Shell fixed by the right valve, irregular, without a pallia! sinus, 

 nacreous inside, with a single cardinal tooth in the left valve ; ligament 

 internal, submarginal, with a lithodesma. 



Tertiary to Recent. 



Genus 1. CHAMOSTREA, F. de Roissy, 1825. 



Chamostrea, F. de Roissy, in Blainville, Man. de Malacologie, 1825, 632. 

 Type : C. albida, Lamarck. Cleidothoerus, Stutchbury, 1829. 



Shell inequivalve, attached by the front slope of the convex dextral 

 valve ; hinge with a small cardinal in the left valve, received into a 

 pit in the right valve ; resilium internal, with a long, curved litho- 

 desma. 



Distribution. Australasia ; one species only. 



Fossil in the Tertiary. 



1. Chamostrea albida, Lamarck, 1819. Plate 61, figs. 13, a. 



Chama albida, Lam., A.s.V., vi, 1819, 96 ; Hanley, Cat. Rec. Biv. Shells, 227. 

 Chamostrea albida, Lam. : Reeve, Conch. Icon., xiv, pi. 1, f. 1 ; Wood- 

 ward, Fischer, Man. Moll., pi. 23, f. 14 ; Ad. G.R.M., iii, pi. 98, f. 4 

 C.M.M., 62 ; M.N.Z.M., 138 ; Hutton, P.L.S. N.S.W., ix, 517 ; Index, 87 ; 

 Tryon, Struct. & Syst. Conch., iii, 202, pi. 117, f. 16, 17. Cleidothcerus 

 chamoides, Sowerby, Genera, f. 1-3 ; Stutchbury, Zool. Journ., v, 1835, 

 98, pi. 42 bis. C. albidus, Lam., A.s.V., eel. 3, ii, 684. 



Shell very solid, inequivalve and inequilateral, the right attached 

 valve hollowed, more or less carinated, the left upper valve slightly 

 convex, fulvous, concentrically lamellated. Beaks anterior, subspiral. 

 Anterior end a little convex, excavated below the umbones ; pos- 

 terior end flatly convex, the dorsal margin rounded and descending ; 

 ventral margin produced, sometimes sharply angled. Sculpture con- 

 sisting of dense lamellar striae. Colour yellowish -brown. Interior 

 light - greenish, somewhat pearly, the posterior margin with a few 

 radiate rays. Margins smooth, thick, but sharp. Hinge with an 

 erect cardinal tooth in the left valve ; resilifer subumbonal, deep, 

 elongated, larger in the right valve, the resilium of the 2 valves con- 

 nected by a long, curved lithodesma. Ligament wanting. Adductor- 

 scars unequal, the anterior very high and narrow, the posterior only 

 half as high, broader, oval. Pallial line distant from the margin, 

 truncated posteriorly. 



Diameter Ant. -post., 58 mm. ; dorso- ventral, 65 mm. : thickness, 

 35 mm. 



Animal Hancock, A.M.N.H. (2), x, 1852, 106, pis. 3, 4 ; Deshayes 

 P.Z.S., 1853, 167 ; Hutton, T.N.Z.I., xiii, 204. 



Type in the Mus. Hist. Nat.. Geneva. 



Hob. North Island of New Zealand, as far as Cook Strait ; Chat- 

 ham Islands : attached to rocks, from low-water mark to about 5 

 fathoms. Also Australia and Tasmania. 



Fossil in the Pliocene and Miocene of New Zealand ; Muddy Creek 

 beds, Soiith Australia. 



