316 Viscount d'ARCHiAC and M. de Verneuil 



in the Devonian beds of the banks of the Rhine. The PterincBce, widely dissemi- 

 nated during the Silurian epoch, particularly in the grauwacke of the Rhenish 

 province and in the state of New York, become rarer in the beds of the middle 

 period in Devonshire and the Eifel. Two species of this epoch are common to the 

 preceding system, and five are reckoned in the Carboniferous period in Belgium 

 and at Ratingen. The AviculcB, on the contrary, increase from below upwards. 

 Seven are mentioned in the lowest system in England, in the north of France, in 

 the grauwacke of the banks of the Rhine, and in the Eifel, and also in Scandinavia. 

 One of the most frequent, the A. reticulata, His., passes into the middle system : 

 twenty-three belong to these last-mentioned beds, from Devonshire, the Eifel, Elbers- 

 reuth and the Fichtelgebirge ; and twenty-four to the upper system of Yorkshire, 

 Belgium, the banks of the Rhine, and Silesia. The Posidonia, whose generic charac- 

 ters are still so ill-defined, are found lower down in the series in North America * 

 than in Europe, where they begin to appear only in the Devonian system of Elbers- 

 reuth. They are particularly abundant in the culm-measures of Devonshire, and 

 in the carboniferous slates of the banks of the Rhine. The P. Becheri, Bronnf, is 

 the most common of these latter. 



The increase in number of species from the lower to the upper beds is still more 

 decided in the Pectines than in the Avicula, for only two are known in the Silurian, 

 even if the grauwacke of Glatz in Silesia does really belong to the first system ; but 

 fourteen species are found in Devonshire, the Rhenish provinces, and the Volkof ; 

 and thirty-two in the Carboniferous system of the north and west of England, in 

 that of Belgium, the banks of the Rhine, Silesia, the Valdai hills and Vitegra in 

 Russia, and even in the province of Bolivia in the centre of South AmericaJ. 



Thus four genera alone had acquired any importance during this long series of 

 deposits, and we much doubt if the family of the Ostracea, as well as the great 

 genera Lima and Spondy lus, vfh'ich, setting off from the Muschelkalk, have been' 

 increasingly developed until the present time, had any real representatives in the 

 ancient seas before the Zechstein epoch. It is in limestones above the true Carboni- 

 ferous system, but yet containing Producti and Spiriferi, that one of us has this year 

 discovered an Ostrea near Arzamas, in Russia §. As to the numerically specific 

 increase of the Conchifera monomyaria in the three systems, it is represented by the 

 numbers 33, 60, and 77 ; of these, three species are common to the first and 

 second system, and five to the second and third. 



VII c. Brachiopoda. — If the Mollusca monomyaria and dimyaria are in these ancient 



* New York States Geological Report, 1840, p. 4:54: 



■f Leonhard's Zeitung fur Miner. 1828. J D'Orbigny, Voyage dans TAmerique meridionale. 



§ This and other facts before alluded to in Russia are explained in a memoir by Mr. Murchison, M. 

 de Verneuil and Count Keyserling, now in course of reading before the Geological Society of London, — 

 March 184'2. 



