146 ETHERIA. 



to a bivalve shell when the valves are equal to each other in 

 dimensions. 



ERATO. Risso. Fam. Convoluted Lam. — Descr. Ovate, more or 

 less angulated, smooth or granulated, with a dorsal scar ; 

 spire short ; aperture large, angulated, emarginated ; columella 

 slightly crenated ; outer lip reflected, denticulated on the inner 

 edge. Suture of the whorls covered with enamel. — Obs. This 

 genus of shells resembles Marginella in form, but has no folds 

 on the columella. Having a scar or groove down the back it may- 

 be considered intermediate between Marginella and Cypraea. Fig. 

 454, E. Maugerise. In the Author's Conchological Illustrations, 

 seven species are enumerated and figured. 



ERUCA. Sw. A subgenus of Clausilia. Sw. Malac. p. 334. 



ERVILIA. Turt. A genus described as " oval, equivalve, equila- 

 teral, closed. Hinge with a single erect tooth closing between two 

 small diverging ones in the opposite valve : lateral teeth none. 

 Ligament internal. E. nitens. Turt. Mya. nitens, Auct." 



ERYCINA. Lam. Fam. Mactracea, Lam. Conchacea, Bl. — Descr. 

 Ovate or triangular, transverse, equivalve, inequilateral, smooth ; 

 hinge with a ligamentary pit, two diverging cardinal and two lateral 

 teeth in each valve ; muscular impressions two in each valve ; pal- 

 leal impressions sinuated. East and West Indies and Mediterranean. 

 — Obs. This genus is distinguished from Mactra and Lutraria by 

 the cardinal teeth being placed one on each side of the ligamenti- 

 ferous pit ; whereas in the last named genera they are both placed 

 on the anterior side. Fig. 86, E. Plebeja. 



ERYTHR^IA. The ancient name for Cypr^a. 



ESCUTCHEON. The impression on the posterior dorsal margin 

 of some bivalve shells. That on the anterior margin is named 

 the lunule. The escutcheon is pointed out by the letter e in 

 some of the figures of Cythereae. Fig. 1 17, a. b. c. 



ETHERIA. Lam. (JEther, air.) Fam. Chamacea, Lam. and 

 Bl. — Descr. Irregular, inequivalve, inequilateral, foliaceous, 

 pearly within, covered by an olive green epidermis without ; hinge 

 callous,- undulated, destitute of teeth ; ligament partly external, 



