GINGLYMACONCHA. OSTREADZ. 349 
Genus 71. OstrREA. 
Ostrea, Pliny, Linneus, Lamarck, Cuvier, &c. 
Perolis, Poli. 
Shells inequivalve, irregular ; the umbones externally dis- 
joined, rather divaricating in the adult state, very unequal ; the 
right valve smaller and flattened, gradually increasing poste- 
riorly, during the life of the animal; the hinge toothless ; the 
ligament half internal affixed to a fossula or little excavation of 
the valves: the fossula of the right valve increases with age, 
and sometimes extends equally with the left umbo itself. 
The lobes of the mantle are only united above the head ; 
their margins with a double fringe. 
1. OsTREA EDULIS. 
Shells with their valves ovately-rounded, the upper margin 
somewhat attenuated behind, with testaceous, concentric, un- 
dulated membranes ; the right valve flattened ; the epidermis 
dirty-fuscous. 
Ostrea edulis, Rondel. Aquat. u. 37; Lister, Anim. Ang]. t. iv. 
f, 26; Conch. ui: t. Ixvii. f. 30; t. exciv. f. 31; Linn. 
Faun. Suec. 2149; Syst. Nat. xii. 1148. no. 211; Sibbald, 
Mus. Balf. 161; Wallace, Ork. 42; Leigh, Lane. 134; 
Smith, Cork, 318; Borlase, Cornw. 274 ; Wallis, Northum. 
390; Dale, Harwich, 383; Gualt. Test. t. ci. f. A, B.; 
Knorr. Vergn. ii. t. xxiv. f. 2. t. xxv. f. 2; Guann. Adriat. 
H.texvin. f. 137; Baxter, Op: subsec. nu. 62. t. vuif.. 1; 2, 
8,9; Penn. Brit. Zool. iv. 102. t.. Ix. -f..70, inf.; Da 
Costa, Brit. Conch. 154. t. u. f. 6; Chem. Conch. viii. 74. 
t. Ixxiv. f. 682; Gmel. Syst. Nat. 3334; Schroét. Einl. 
Molo; Brug. Encycl. Méth. t.. elxxxiveifoc/, 8; <Pulk 
Cat. Dorset. 36. t. u. f. 6; Mont. Test. Brit. 151; M. & 
R. Trans. Linn. Soc. viii. 102; Flem. Edinb. Encyel. vii. 
98; Dill. Desc. Cat. 280; Turt. Conch. Dict. 133. 
Varietas pygmzea. Ostrea parasitica, Turt. Conch. Dict. 134. 
This species is extremely common in the European seas, 
‘n estuaries, friths, and the mouths of rivers. 
