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The other, Archaeocidaris, represents, in like manner, the Cidaris of the present seas. Productus semireticulatus, Martin, sp. Spirifera trigonalis, Martin, sp. Mountain Limestone. Spirifera glabra, Martin, sp. The British Carboniferous mollusca enumerated by Mr. Etheridge comprise 653 species referable to 86 genera, occurring chiefly in the Mountain Limestone.
There are 25 Gasteropods and only one cephalopod, Nautilus Freieslebeni, which is also found in the German Zechstein. Spirifera alata, Schloth. Syn. Trigonotreta undulata, Sowerby., King's Monograph. King and Howse.
The place of the sandstones of the Foreland is not yet clearly made out, as they are cut off by a great fault and disturbance. Spirifera disjuncta, Sowerby. Syn. Sp. Verneuilii, Murch. Phacops latifrons, Bronn. Clymenia linearis, Munster. The fossils are numerous, and comprise about 150 species of mollusca, a fifth of which pass up into the overlying Carboniferous rocks.
G.B. Sowerby, and have been described by him: they consist of two species of Producta, and of six of Spirifera; two of these, namely, P. rugata and S. rotundata, resemble, as far as their imperfect condition allows of comparison, British mountain-limestone shells. Mr. Lonsdale has had the kindness to examine the corals; they consist of six undescribed species, belonging to three genera.
This is by no means a rare fossil in the slaty limestone of South Devon, and, like the Eifel form, is confined to the middle group of this country. Spirifera mucronata, Hall. Among the 18 species of all classes enumerated by Mr. Etheridge, two-thirds are common to the Middle Devonian, but only one, the ubiquitous Atrypa reticularis, can with certainty be identified with Silurian species.
The size of these septa is enormous compared with those of any other brachiopod shell; and they must nearly have divided the animal into two equal halves; but they are, nevertheless, of the same nature as the septa or plates which are found in the interior of Spirifera, Terebratula, and many other shells of this order. Messrs.
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