2l6 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



system. Even the Khizopoda (Foraminifera), which have so wide a 

 distribution in time, occur not beyond the limits of this formation. 



Lamellibrancrtata. — Monomyaria*. This group and the Dimy- 

 aria united number no less than 54 genera and 415 species. The 

 Monomyaria, up to the present time, are represented by 10 genera 

 and 179 species, 103 of which belong to the genus Aviculopecten, 28 

 to Avicula, Pinna 6, Posidonomya 12, Pterincea 4, Pteronites 9, Stre- 

 blop>ieria 3, Gervillia 2, Inoceramus 4, Lima 2, and Pinna 6. The 

 Calciferous Sandstones of Scotland and Northumberland have yielded 

 3 genera {Avicula, Aviculopecten, and Pteronites) and 13 species : 

 the Lower Limestone Shales, or Lower Limestones, 5 genera and 64 

 species ; the Carboniferous Limestone 11 genera and 151 species ; 

 the Toredale rocks 4 genera {Avicula, Aviculopecten, Pinna, and 

 Posidonomya) and 14 species ; the Millstone Grit 3 genera {Avicula, 

 Aviculopecten, and Posidonomya) and 11 species; the Lower Coal- 

 measures 3 genera (the same) and 13 species ; 4 species of Aviculo- 

 pecten occur in the Middle Coal-measures ; and 1 {Aviculopecten papy- 

 raceus) is the only form in the Upper Coal-measures. The species 

 having the longest range are Aviculopecten alternatus, A. gentilis, A, 

 granosus, A. papyraceus, A. quadratus, A. scalaris, and A. variabilis, 

 Posidonomya Becheri, P. lateralis, and P. membranacea. The species 

 of the genera Pteronites, Pterinma, Streblopteria, Posidonomya, Pinna, 

 Avicula, and most of the Aviculopectines are chiefly from the Car- 

 boniferous Limestone. We may assume that the largely represented 

 group of the Avieulopectinidse possessed much the same bathymetrical 

 range as that of the genus Pecten in our modern seas ; the same with 

 Pinna and Posidonomya. Indeed it would appear, from the per- 

 sistency of the vertical range of the group Monomyaria, that no 

 general depth governed their habit ; for only 14 species out of the 179 

 range above the Carboniferous Limestone and Yoredale beds. 10 are 

 named above ; and the following 4 may complete the species — Avicu- 

 lopecten fibrillosus, A. obtusus,Posido7iomya Gibsoni, and Pinna spatula. 

 The Table also expresses the number of species that are in the Mill- 

 stone Grit and Coal-measures included here. The magnitude of the 

 Monomyarian group is sufficient reason for treating it separately, 

 especially considering that one genus alone {Aviculopecten) is repre- 

 sented by 103 species. 



* I retain this term here, including in it only the Asiphonida, represented by 

 the Ostreida?, Aviculidce, and Pectinidse. 



