on the Fossils of the older Deposits in the Rhenish Provinces. 319 



The species peculiar to the middle system have very seldom been found identical 

 in many distant regions, and the same may be observed in regard to those of 

 the superior or Carboniferous system. The 0. Umbraculum, as it is defined by M. 

 de Buch, seems to bind together the Devonian and Carboniferous systems in seve- 

 ral parts of Europe, and the 0. rugosa {Leptcena, Dalm.) the two inferior systems 

 on this side of the Atlantic, as well as on the other, where it is found in the 

 Catskill Mountains, in the beds of Trenton Falls, and in Pennsylvania. 



The species for which we have provisionally retained the generic names of Del- 

 thyris and Cyrtia are all Silurian, and from Scandinavia and the state of New York. 



The Spiriferi * present, so to speak, an intermediate distribution between that of 

 the Producti, the number of which increases very rapidly in the superior system, and 

 the Terehratula, the species of which are almost equally disseminated in the three 

 systems. In the same manner, the Spiriferi increase from below upwards, but follow 

 a much less rapid progression than that of the Producti, being represented by the 

 numbers 29, 50 and 74. There are but few species exclusively Silurian, which 

 are found throughout a certain extent of country, and consequently may be re- 

 garded as really characteristic of the inferior system. In the middle system we 

 find the S. heteroclites (de Buch) in Devonshire and on the right bank of the Rhine ; 

 the S. speciosus (Schlot.) in Devonshire, Belgium, the Eifel, Russia, the Ural, and 

 in the Cedar Mountains north of the Cape of Good Hope ; the Sp. Verneuilli 

 (Murchisonf) in the Bas Boulonnois, Belgium, Voroneje in Central Russia, and 

 as far as Smeinogorsk and Berosowa in the Altai'. The species exclusively Car- 

 boniferous are very numerous in the mountain limestone of England and Belgium, 

 and a few of them extend to the several basins of Russia, where they occur with 

 other peculiar species, and M. d'Orbigny has found some of them in beds of the 

 same age in South America. The Spiriferi of the Carboniferous system are in general 

 distinguished by their less numerous, wider and more rounded, and frequently dicho- 

 tomous plaits. The species also attain greater dimensions, are more commonly glo- 

 bular or rounded in form, and are generally smoother than in the older formations. 

 Among the Spiriferi common to two systems, we may mention, as being both Silurian 

 and Devonian, the Sp. trapezoidalis {Cyrtia, Dalm.), which is found in England, in 

 Belgium, upon the banks of the Rhine, in Scandinavia, and in the north of Russia ; 

 and the Sp. macropterus (Goldf.), from the Eifel, the Rhenish provinces, Russia, 

 Kunawur in the Himalaya J, the Cedar Mountains in the south of Africa, the state 

 of Ohio, and the lower Silurian beds of the state of New York. The latter is the 



* We have united Trigonotreta to Spirifer. f Bulletin Geol. Soc. de France, tome xi. 



X Dr. Royle's Illustrations of the Botany, &c., of the Himalaya Mountains, Part XI. Fossils, pi. 3. 

 f. 23, and p. xxix. 



2x2 



