MAZATLAN BIVALVES 63 
1s somewhat nearer to the hinge, with the sinus less ascending. 
Epidermis extremely thin. Long. 1°51, lat.1°54, alt. ‘8. 
Hab.—St. Elena, West Columbia [?] very rare, Mus. Cuming. 
(Hanl.)—Panama, extremely rare; C. B. Adams.—Mazat- 
lan; Lieut. Green.—Mazatlan, extremely rare; L’pool Col. 
Tablet 266 contains the largest specimen. 
Genus DIONE, Megerle. 
Dione, B. M. Cat. Ven. p. 54. =Cytherea (maxima pars), Lam. 
Known by the smooth posterior teeth, ovate transverse form, 
and large horizontal pallial sinus. 
92. Dione aurantia, Hanl. 
Cytherea aurantia, Hanl. Sp. of Shells, Append.: Wood Suppl. 
pl. 15, f. 20.—Sow. Thes. Conch. p. 228, pl. 132, f. 97 bis. 
Chione aurantia, Gray, Analyst, viii. 305. 
Dione aurantia, Desh B. M. Cat. Ven. p. 56, no. 3. 
Cytherea aurantiaca, Sow. Gen. f. 3.— Rve. Conch. Syst. pl. 69, 
f, 3.—Jay’s Cat. p, 35.—C. B. Ad. Pan. Shells, p. 272, no. 44A. 
This magnificent and typical species appears to belong to the 
N. W. tropical province. The shape in regularity more nearly 
coincides with D. chione than with D. chionea. It is however 
larger and heavier; less transverse, lunule less marked, and 
shewing a tendency to irregular concentric ridges of growth. 
The trifureate white mark at the umbos has shorter and broader 
rays. The colour is a light salmon with occasional concentric 
bands of darker, in the young shell generally white at the 
margin; covered with a uniform, rather thin, adherent, dark 
orange epidermis. Inside white, with purple stain on the liga- 
mental portion. Anterior adductor deeply impressed: the 
rest nearly as in D.chione. I have not been able to trace 
Sow.’s “obscure biangulato, &c.”’ copied by Desh. Long. 3°62, 
lat, 4°28, alt, 2°37. A specimen from 8. W. Mexico is some- 
what larger. 
Hab.—Gulf of Nicoyia, Jay.—Taboga, very rare, C.B. Adams.— 
South America [?; non D’Orb. nee Cum.]; Acapulco; Desh- 
ayes.—S. W. Mexico, P. P. C—Mazatlan; Lieut. Green. — 
Do. not common; L’pool Col.* 
* **Brazil;” Manchester Mus., without authority ; probably an error, 
