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The vast longevity of such specific forms has not been generally recognised in consequence of the change of names which they have undergone when derived from such distant formations, as when Atrypa unguicularis assumes, when derived from a Carboniferous rock, the name of Spirifer Urei, besides several other synonyms, and then, when it reaches the Permian period, takes the name of Spirifer Clannyana, King; all of which forms the author of the monograph, now under consideration, asserts to be one and the same.
Murchison and De Verneuil discovered this species dispersed in myriads through a white limestone of Upper Silurian age, on the banks of the Is, on the eastern flank of the Urals in Russia, and a similar species is frequent in Sweden. Lingula Lewisii, J. Sowb. Atrypa reticularis, Linn. Upper valve. b. Lower valve. c.
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.
This deposit contains numerous fossil shells, consisting chiefly of four distinct species of a new genus, nearest to hippopodium; also a new species of trochus; Atrypa glabra, and Spirifer, a shell occurring also in older limestones of England.* These shells having been submitted to Mr. James De Carl Sowerby, I am indebted to that gentleman for the following description: Class Conchifera.
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