Physical Geography. 147 



If we now turn to the assemblage of shells we shall 

 find it to be very poor in number. In the red marls and 

 bands of Magnesian Limestone at and near Manchester, 

 the very few species found in the marls and thin lime- 

 stones are poor and dwarfed in aspect, and in this re- 

 spect, and the small number of genera they somewhat 

 resemble the living molluscan fauna of the Caspian 

 Sea. 



In the true Magnesian Limestone district of Notting- 

 hamshire, Yorkshire, and Durham, the case is somewhat 

 different. There we find a more numerous molluscan 

 fauna, but wonderfully restricted when compared with 

 that of Carboniferous Limestone times. I give it in 

 some detail, that the reader may judge for himself, as 

 the facts have an important bearing on my argument. 

 The numbers are taken from Mr. Etheridge's forth- 

 coming work. 



BRACHIOPODA. Camarophoria 3, Crania 2, Discina 

 1, Linyula 2, Producta 2, Spirifera 3, Spiriferina 2, 

 Strophalosia 4, Terebratula 2 : in all, 9 genera and 21 

 species. 



LAMELLTBRANCHIATA. Aucella 1, Mytilus 2, Avi- 

 cula 2, Gervillia 5, Area 2, Cardiomorpha 1, Cteno- 

 donta 1, Leda 1, Myalina 1, Myochoncha 1, Pleuro- 

 phorus i, Edmondia 1, Astarte 2, Schizodus 5, 

 Solemya 4, Tellina 1 : in all, 16 genera and 31 species. 



UNIVALVES. Calyptrcea 1, Chemnitzia 1, Chiton 

 3, Chitonellus 4, Dentalium 1, Natica 2, Pleuroto- 

 maria 3, Rissoa 1, Straparolus 1, Turbo 5, Turbo- 

 nilla 4 : in all, 1 1 genera and 26 species. 



PTEROPODA. Theca 1. 



CEPHALOPODA. Nautilus 1 . 



The whole comprises only 38 genera and 80 species, 

 a very poor representative of the teeming life in the Car- 



L 2 



