266 



DISTINCTIVE CHARACTERS. 



have existed there. At present this form occurs 

 in wonderful profusion in our Celtic province, more 

 sparingly in the north Lusitanian, is scarce in the 

 south Lusitanian province, is not found about the 

 Atlantic islands, nor in the Mediterranean. 



Tracing back the history of this species in time, 

 it cannot be admitted into the fauna of the crag 

 period, nor into that of the Faluns of Touraine — 

 nor yet into any member of the Italian tertiary 

 series. It makes its first appearance in the upper 

 Faluns of Dax, under its commonest form, but by 

 no means as a common shell. At this period the 

 Patella vulgata must have been at its numerical 

 minimum in European latitudes. 



This form is at its numerical maximum now, as 

 an element in the existing fauna of the European 

 seas j it is referable to the temperate Atlantic (its 

 specific centre is on the west coast of Ireland). It 

 has a less southern range than it had before the 

 communication with the Arctic basin was esta- 

 blished ; and it is since that physical change that 

 it has found those conditions which have so fa- 

 voured its numerical increase. 



In all future time, Patella vulgata, in its profuse 

 abundance, and numerous varieties, will characterize 

 the deposits of a definite portion of the area of the 

 existing European seas ; and it will, moreover, have 

 its definite place in the newer tertiary series. Many 

 of our common species, when considered with refer- 

 ence to their range in time, and their distribution 



