(b) Bivalvia (= Conchae): Mya, Solen, Tellina, Cardium, Mactra, Donax, Venus, Spondylus, Chama, Arca, Ostrea, Anomia, Mytilus, Pinna.
The Senonian consists of a central facies with Micraster peini; a meridional facies with Ostrea; and a northern facies developed round Tunisia with large forms of Inoceramus and echinoids.
The Middle Eocene is characterized by the presence of Ostrea bogharensis and the Upper Eocene by highly fossiliferous sandstones and marls.
At the close of the Lower Miocene period (beds with Ostrea crassissima) great modifications in the relief and limits of the Algerian formations took place.
- Development of the Oyster, Ostrea edulis.
It has been conclusively shown that the Ostrea edulis does not fertilize itself.
d irpEov, oyster, so called from its shell, 66TEOV, bone, shell) in zoological nomenclature; there are no genera so similar to Ostrea as to be confounded with it in ordinary language.
Ostrea is a genus of Lamellibranch Molluscs.
in what follows the species of the European coasts, Ostrea edulis, is under consideration.
The genus Ostrea has a world-wide distribution, in tropical and temperate seas; seventy species have been distinguished.
Westward of and above these strata, the Middle and Upper Jurassic formations are found (Lias, Lower Oolite, Oxfordian, &c.), with well-marked and numerous fossils (Ammonites, Nerinaea, Natica, Astarte, Rhynchonella, Echinodermata, &c.); then the Cretaceous rocks, both these and the Jurassic series being largely developed, the Cretaceous fossils including Nautilus, Belemnites, Ostrea, Gryphaea, &c., and some very large Ammonites (Pachydiscus).
In the Coralline Limestone the following fossils have been noted :- Spondylus, Ostrea, Pecten, Cytherea, Arca, Terebratula, Orthis, Clavagella, Echinus, Cidaris, Nucleolites, Brissus, Spatangus; in the Marl the Nautilus zigzag; in the Yellow, Black and Greensand shells of Lenticulites complanatus, teeth and vertebrae of Squalidae and Cetacea; in the Sandstone Vaginula depressa, Crystallaria, Nodosaria, Brissus, Nucleolites, Pecten burdigallensis, Scalaria, Scutella subrotunda, Spatangus, Nautilus, Ostrea navicularis and Pecten cristatus (see Captain Spratt's work and papers by Lord Ducie and Dr Adams).
In the Ostrea edulis fertilization of the eggs is effected at the moment of their escape from the uro - genital groove, or even before, by means of spermatozoa drawn into the sub-pallial chamber by the incurrent ciliary stream, and the embryos pass through the early stages of development whilst entangled between the gill-lamellae of the female parent (fig.
The use of this name in the vernacular is equivalent to that of Ostrea (Lat.
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