Mollusca aut. 



1. Class. Pelecypoda Goldf. 



(Acephala Cuv., Lamellibranchiata Blv.) 

 I. Ordo. Tetrabranchia FlSCHER. 



Utrinque branchiae binae, externa supra internam posita, lamina accessoria 

 (appendice) praedita aut ea carens. 



1. Subordo. Ostreacea (Stol.) Fisoher. 



Pallium omnino apertum , siphones nulli , musculus adductor singulus , sub- 

 centralis aut posticus ; branchiae 4 aequales ; pes millus aut rudimentaris et byssi- 

 fer ; cor intestino recto non pertusum ; testa lamellosa aut cellulosa , sine strato 

 flbroso, inaequivalvis, plerumque pleuroconcha ; ligamentum internum; cardo edentu- 

 lus; linea pallialis integra. 



1. Fam. OSTEEIDAE Gray. Pes nullus; musculus adductor e partibus 

 duabus constans ; branchiae post inter se et cum pallio connatae ; testa plerum- 

 que inaequivalvis, sinistra aftixa; umbones subcentrales aut curvatl. 



Ostrea L. FaUium marginatum , papillosum, branchiae subaequales, postice 

 unitae; labia sittiplicia, palpi triangulares , affixi; testa irregularis, valva sinistra 

 major affixa, dextra plana aut concava; rostrum valvae sinistrae saliens, contortum, 

 antrorsum aut rctrorsum involutum; area ligamentalis triangula aut elongata, sym- 

 inetrica. 



Subg-en. Ostrea JIorch {Alectryonia Fisch. de W.). Valvae longitudine 

 quasi subaequali, margine laevi aut denticulato, superficie laevi aut plicata. 



1. 0. edulis L. (0. (lefomiis Lam. , 0. parasitica Turt.). Testa ovato- 

 rotundata, apicem versus subattenuata, compressa, crassa, extra foliacea, lutescenti- 

 fusca ; umbonibus parvis , cartilagine divisis ; facies interna alba , margaritacea, 

 impressio muscularis oblique transversa, piriformis. — Diam. 75 — ^120 mm. 



Distrib.: Mare Germanicum, Britannicum, Atlanticum. — Fossilis in stratis 

 tertiariis et posttertiariis. 



var. a) crassa, himellis appressis (0. Mppoims Lam., var. 0. tarentina Issel). 



var. b) minor, planior, purpurascens aut viridi-brunnea (0. parasitica Turt.). 

 (Cabo di Gata, Cartagena, „Porcupine" Jeffreys.) 



Prorsus incertum est, de qua forma agitur in rehitionibus autorum locos 

 specierum indicantibus. Verisimile est, fere ubique varietatem a) dictam esse. 



Habit. : Gibraltar (MacAndrew, Jepfreys); Malaga (MacAndrew, Rosen- 

 hauer), Valencia, Barcelona (Hidalgo); ins. Balear. : Menorca (Ramis), Alcudia, 

 Adayo (Hidalgo), Mahon (MacAndrew, Cardona); Alger (Weinkauff); litora 

 Galliae: Roussillon (Locard), La Franqui (P£i'katx), Cette (Granger), Palavas, 



