318 TESTACEOUS MOLLUSCA. 
Smooth, rather thin; apex distant from the margin; disk of ad- 
hesion oblong, not close to the dorsal margin; perforation short, 
situated near the dorsal end of the disk of adhesion. 3. Chili. 
D. (O.) Tenurs. Sow. Th. 1, p. 266, t. 73, f. 4, 5. Smooth, thin, 
apex of the upper valve near the dorsal margin; disk of adhesion 
obtusely triangular, close to the dorsal edge; perforation linear. 3. 
D. (O.) Cuminent. Brod. Z. P. 18338, p. 124;. Z. T. 1, t. 28, f. 1. 
—Desh. ed. Lam. 7, p. 317.—Sow. Th. 1, p. 366, t. 73, f.6. Nearly 
orbicular, subconical, rather thick, with numerous striz radiating 
from the subcentral apex and decussated by the elevated lines of 
growth; epidermis pale brown. 4. Mazatlan, near Panamna. 
D. (O.) Srrrara.— Discrna Osrreomes, Lam. (no definition).— 
O. Norweaica (not Lam.), Sow. Tr. Lin. 13, pl. 26, f. 2—Sow. G. 
Reeve, Syst. t. 129, f. 3, 4,5.—D. N., Crouch, t. 18, f. 2.—O. S., 
Sow. Th. 1, p. 366, pl. 73, f.8. Rather irregularly orbicular, thickish ; 
apex nearly central; upper valve with numerous elevated striz from 
the apex to the margin. 3. Mr. Sowerby appears to have changed 
the name from a not unreasonable doubt of the implied locality. 
Lamarch’s pictorial definition of O. NonRwEGIcA points to Crania N. 
Hab. ? 
D. (0.) Striegata. Brod. Z. T. 1, t. 23, f. 1—Sow. Th. 1, p. 366, 
t. 73, f. 7. Rather thick, nearly orbicular, slightly striated, radi- 
atingly streaked with chestnut-colour; epidermis thin, pale brown. 
as. Guatemala.* 

THECIDIUM.? 
Small, thick, punctated, inequivalve, Terebratula-like ; the larger 
valve attached by the produced umbo, which is imperforate when adult. 
Smaller valve flattened, opercular ; hinge-area flat, triangular ; interior 
almost filled by a complicated apophysis. 
T. MeprrerraNeumM.—THecipEA M., Risso, p. 394, f. 183.—Desh. 
Lam. 7, p. 846.—Phil. 1, p. 99, t. 6, f. 17.—Tuecipium M., Sow. G. 
— Reeve, t. 127, f. 6, 7—Sow. Th. 1, p. 371, t. 73, f. 30, 1, 2.— Gray, 
Brach. p. 118, f. 126.— Woodw. f. 128.—T. Sponpytea, Scacchi. 
Small, pale yellow, smooth, subquadrate, slightly bilobed ventrally, 

« See, too, the O. Evanstt of Davidson (7. P. 1852, t.14, f. 32, 3, 4), 
and the O. AnrittaruM, D’Orb. Mol. Cub. 
2 Turcipra of Defrance, admitted as a genus by Deshayes. The 
internal appendage has been thus described :—* Disk grooved for the 
reception of the loop, the grooves separated by branches from a 
central septum; loop often unsymmetrical, lobed, and united more 
or less intimately with the sides of the groove.” 
