OF CONCHOLOGY. 75 



Genus Trematis,* Sharpe, (= Orbicella D'Orb., 1. c.) 



Upper valve with a posterior apex and small false area. 

 Lower valve flattened, with a large foramen" extending nearly to 

 the posterior border. Shell structure in two layers, the outer 

 calcareous, with a peculiar reticulated sculpture. Inner layer 

 horny, minutely tubulous as in Discina. Type Orbicula termin- 

 alis, Conrad, in Nat. Hist. N. Y. Part iv, Geology, by Emmons, 

 p. 395, f. 4, 1842. 



I am not prepared at present to admit Siphonotreta and Acro- 

 treta into this family, but incline to the opinion of Kutorga, that 

 they form a group by themselves. 



Keyserlingia, Pander (Bull. Ak. Sci. St. Petersb. iii, p. 46, 

 1861. Type K. reversa, Pand. PI. ii, f. 1, a — g.) appears to 

 have relations with Siphonotreta, but its position is at present 

 doubtful. 



Genus DISCINA, Lam. 



Discina, Lamarck, Hist. An. Vert, vi, p. 236, 1819. 

 = Crania, /3., Schumacher, Essai, p. 102, 1817. 

 = Orbicula, Sowerby, Min. Conch vi, p. 4, PI. 506, 1830. 

 = Orbicula, sp., Lamarck and Owen. 



Not Orbicula, Cuvier, Tabl. Elem. Regne An. p. 435, 1798, 

 Lam. An. s. Vert, i, vi, pt. i, p. 242, 1819, Schum. Essai. p. 55, 

 1817,= Crania. 



Type Discina striata, Schum. sp. 



— Crania (/3) striata, Schum. Essai, p. 102, PL xx, f. 1, a — f. 



1817. (Not 0. striata, Defrance). Hob. ? 

 = Crania radiosa, Gould., 1852. Hab. Cape Palmas. 

 = Orbicula striata, Sowerby, Thes. Conch, i, p. 366, PL 73, f. 



9, 1847. Forbes and Hanley, Brit. Moll, ii, p. 368, 



1853. 



— Orbicula norvegica, Sowerby, Tr. Lin. Soc. xiii, p. 468, PL 



xxvi, f. 2, 1823. (Syn. exclus.) N. Africa. 

 = Discina ostreoides, Lamarck, An. s. Vert, vi, p. 237, 1819. 



No description. 

 = Orbicula ostreoides, Reeve, Conch. Icon. PL i, f. 7 a, b. 

 = Orbicula Evansii, Davidson, P. Z. S. 1852, p. 81, PL xiv, f. 

 32 — 34. Hab. Bodegas, Cala. in error. 

 Not Orbicula striata, Sowerby, Silurian Syst. t. v. fig. 21, 

 1839, and Siluria PL xx, f. 3. 1859, a fossil species. 

 Not Orbicula norvegica, Lamarck, = Crania anomala. 

 Not Discina osti-eoides, Turton, Dith. Brit. p. 238, 1822. 



* Quart. Journ. Geol. Soc. No. 13, vol. iv, p. 66, June, 1847. 



