on the Fossils of the older Deposits in the Rhenish Provinces. 315 



system there are seven species, of which one, the C. aliforme, Sow., is common to 

 the preceding system, and is found in Ireland, England, Belgium, and at Elbers- 

 reuth. Lastly, Isocardia and Cypricardice also appear occasionally in the several 

 systems. We must further observe, that the greater part of the Cardiacecs of these 

 ancient seas are of much smaller dimensions than in those of the following periods, 

 in which the species attained (like the greater part of the Acephali) larger and larger 

 dimensions without presenting on that account less varied forms. 



There is nothing very particular about the Nuculce of this epoch : there are twelve 

 species in the inferior system, mostly in the Silurian grauwacke of the banks of the 

 Rhine, several in England, and others are found in Scania in diluvium ; seven are 

 from the Devonian limestones of the Eifel and Elbersreuth, and fifteen from the 

 mountain limestone of Ireland, England, and Belgium. The CucuUcbcs are particu- 

 larly found in the Devonian beds of the south-west of England, and one of them 

 occurs in the Silurian rocks of the Cedar Mountain in the south of Africa*. The 

 Area, of which one only has been pointed out in the Silurian system, afford three 

 species to the middle system in the Eifel, at Paffrath and at Elbersreuth, and thirteen 

 to the carboniferous limestone of Derbyshire, Belgium, Silesia, and the north of 

 Russia. 



The Megalodontes are peculiarly Devonian ; and one species, the M. cucullatus, 

 Sow., is characteristic of this system in the south-west of England, as well as upon 

 the right bank of the Rhine. The Modioli and Mytili, rare in the Silurian system, 

 are more abundant in the beds which surmount it. These shells are frequent 

 enough in the Orthoceratite and Clymenia limestones of Elbersreuth, as well as in 

 the mountain limestone of England, Belgium, Ratingen, Silesia, and Russia. Two 

 Anodontes are mentioned by M. Eichwald as found in the carboniferous limestone 

 of the coal region of Donetzf ; and of twenty-two species of Unio, twenty-one be- 

 long to the coal-measures of England and Scotland, and of the environs of Liege 

 and Werden. 



Thus it will be seen that the Conchifera dimyaria are irregularly disseminated in 

 the three systems, in which the species of each system are represented in an ascend- 

 ing series by the numbers 49, 145, and 126 ; and of these species nine are Silu- 

 rian and Devonian, and five are Devonian and Carboniferous. 



VII h. Conchifera monomyaria. — The Acephala monomyaria present only a small 

 number of genera in the seas which precede the deposit of the upper new red 

 sandstone or Trias. Count Miinster enumerates nine species of Inoceramus from 

 the limestones of Elbersreuth and the Fichtelgebirge. One of them, the In. vetus- 

 tus, Sow. J, is found also in the mountain limestone of Yorkshire, Belgium, and 



* Mr. Murchison, Silur. Syst. p. 653. t Jahrb. fur Min. 1840, p. 732. 



X This shell, according to the observations of M. de Koninck and our own opinion, should be consi- 

 dered a Posidonia (June 1842). 



