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Among other characteristic shells are Pecten Hoeninghausii, and a species of Cassidaria, and several of the genus Pleurotoma. The succession of the Lower Miocene strata of Belgium can be best studied in the environs of Kleyn Spawen, a village situated about seven miles west of Maestricht, in the old province of Limburg in Belgium.
I collected sixty shells from the New Jersey deposits in 1841, five of which were identical with European species Ostrea larva, O. vesicularis, Gryphaea costata, Pecten quinque-costatus, Belemnitella mucronata. As some of these have the greatest vertical range in Europe, they might be expected more than any others to recur in distant parts of the globe.
Further inland, with the exception of the superficial gravel, the whole thickness of the truncated hills, which represent a formerly continuous plain 950 feet in height, appears to be formed of this white mudstone: here and there, however, at various heights, thin earthy layers, containing the great oyster, Pecten Paranensis and Turritella ambulacrum, are interstratified; thus showing that the whole mass belongs to the same epoch.
It consists of a horse-shoe arch, the face of which is ornamented with gilded glass mosaic, forming the entrance to a semi-circular recess beautifully adorned with arabesques and inscriptions, the top of the dome being a large white marble slab hollowed out in the form of a pecten shell.
In the mollusc, on the contrary, the retina is derived from the ectoderm directly, and not indirectly by means of the embryonic encephalon. Quite different, therefore, are the evolutionary processes which lead, in man and in the Pecten, to the development of a like retina.
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