on the Fossils of the older Deposits in the Rhenish Provinces. 317 



beds represented only by a feeble development in comparison with that which they 

 exhibit in the secondary and tertiary periods and have since acquired in the present 

 seas, the Brachiopoda, on the contrary, display a variety of forms, an abundance of 

 species, and a profusion of individuals greater than we find in any other epoch. 

 Notwithstanding the constancy of the fundamental type of the animals of this 

 order, the subtypical forms have, during the deposition of the various Palaeozoic 

 rocks, undergone changes and developments often the reverse of each other ; we 

 therefore pause a few moments to consider the interesting and striking relation of 

 these forms with the antiquity of the beds in which they occur. 



The true Producti, which we distinguish from those Brachiopoda provisionally 

 retained by us under the name of Leptana, do not appear to have existed during 

 the Silurian period, either in Europe or in other parts of the globe. Of four species 

 noted in the Devonian system, and found in the south-west of England, in the north 

 of France, in the Eifel, at Refrath, and in Russia, three are common to the Carboni- 

 ferous system. The Pr. subaculeatus, Murch.*, is the most constant in the middle 

 system of the north of France, of Belgium, and of the Eifel, and it extends even 

 into the northern and central parts of Russia. 



This genus, on the contrary, increased so greatly, both in number of species and 

 in dimensions, during the Carboniferous epoch, that it might alone, so to speak, be 

 taken to characterize it ; the Productus Martini, P. antiquatus, P. comoides, P. 

 lobatus, P. giganteus, and P. punctatus, of Sowerby, are profusely disseminated not 

 only through the Carboniferous system in Ireland, Scotland, the north and west of 

 England, in France and Belgium, and on the banks of the Rhine, but also in the 

 basins of northern, middle and southern Russia, upon both flanks of the Ural, and 

 lastly, most of them are found in the carboniferous rocks of North America f. 

 Of seventy-two species of Productus of this period, the greater number are found 

 in the mountain limestone of Yorkshire, Derbyshire, the province of Liege, at Ra- 

 tingen, and in the north of Russia ; but we must also remark, that they do not 

 cease to be observed even in the beds of the coal-measures, as we know that they 

 occur in them at Coalbrook Dalej, or in those districts in which the mountain 

 limestone no longer forms a distinct platform at the base of the Carboniferous sy- 

 stem, but where it is confounded with other coal-measures, as at Sable (France), in 

 the north and south of Russia, and in North America. In the province of Bolivia, 

 M. Alcide d'Orbigny has pointed out nine species of Productus, and he has shown 



* Bull. Geol. Soc. de France, tome xi. p. 255, 1840. 



t The Productus antiquatus is found at Spitzbergen with other carboniferous forms, also in Soutli 

 America, on the shores of Lake Titicaca (April 1842). 



+ See Mr. Prestwich"s Memoir on the Structure of Coalbrook Dale, Geol. Trans., 2nd Series, vol. v. 

 Part 3. 



VOL. VI. SECOND SERIES. 2 T 



