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Cyprides from the Upper Purbeck. a. Cypris gibbosa, E. Forbes. b. Cypris tuberculata, E. Forbes. c. The highest of the three divisions is purely fresh-water, the strata, about fifty feet in thickness, containing shells of the genera Paludina, Physa, Limnaea, Planorbis, Valvata, Cyclas, and Unio, with Cyprides and fish.
Sometimes entire skeletons have been discovered within a few feet of the surface, in peaty earth at the bottom of small ponds, which the agriculturists had drained. The shells in these cases belong to freshwater genera, such as Limnaea, Physa, Planorbis, Cyclas, and others, differing from European species, but the same as those now proper to ponds and lakes in the same parts of America.
"Of Physa and Lymnaea, it is extremely doubtful whether there are any species throughout the province more than we have in Britain.
Now, as none of these last, or the unimuscular bivalves, are fresh-water, we may at once presume a deposit containing any of them to be marine. Planorbis euomphalus, Sowerby; fossil. Limnaea longiscala, Brongniart; fossil. Paludina lenta, Brand.; fossil. Succinea amphibia, Drap. Valvata piscinalis, Mull.; fossil. Physa hypnorum, Linne; recent. Auricula; recent. Melania inquinata, Def.
Among the mollusks, a remarkable ribbed Melania, of the section Chilina, occurs. Ostrea distorta, Sowerby. Cinder-bed. Hemicidaris Purbeckensis, E. Forbes. Cyprides from the Middle Purbecks. a. Cypris striato-punctata, E. Forbes. b. Cypris fasciculata, E. Forbes. c. Physa Bristovii, E. Forbes. It was accompanied by a species of Perna.
Physa columnaris, Desh. Melanopsis buccinoidea, Ferr.; recent. The univalve shells most characteristic of fresh-water deposits are, Planorbis, Limnaea, and Paludina. Neritina globulus, Def. Nerita granulosa, Desh.
The mollusks abound, a peaceful tribe. At the bottom, the plump river snails discreetly raise their lid, opening ever so little the shutters of their dwelling; on the level of the water, in the glades of the aquatic garden, the pond snails Physa, Limnaea and Planorbis take the air.
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