MAZATLAN BIVALVES 63 



is 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. 

 (Hani.) Panama, extremely rare ; C. B. Adams. Mazat- 

 lan ; Lieut. Green. Mazatlan, extremely rare ; Lpool 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. 



-V 92. DIONE AUEANTIA, Hani. 



Cytherea aurantia, Hani. Sp. of Shells, Append. : Wood Suppl. 



pi. 15, f. 20 .Sow. Thes. Conch, p. 228, pi. 132, f. 97 bis. 

 Chione aurantia, Gray, Analyst, viii. 305. 

 Dione aurantia, Desk B. M. Cat. Ven. p. 56, no. 3. 

 Cytherea aurantiaca, Sow. Gen. f. 3. Itve. Conch. Syst. pi. 69, 



f. 3. Jay's Cat. p. 35. C. B. Ad. Pan. Shells, p. 272, no. 444. 



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. chiona3a. It is however 

 larger and heavier ; less transverse, lunule less marked, and 

 shewing a tendency to irregular concentric ridges of growth. 

 The trifurcate 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 S. W. Mexico is some- 

 what larger. 



Hob. 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 ; Lpool Col.*' 



* "Brazil; " Manchester Mus., without authority; probably an error. 



