146 ETHERIA. 



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

 dimensions. 



ERATO. Risso. Fam. Convolutse, Lam. — Bescr. 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 Cyprasa. 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. — Bescr. 

 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. 



ERYTHRiEA. 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 Cytherese. Fig. 117, a. b. c. 



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

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

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

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



