184 



This fiiell differs from the P. pefUnata in colour, and in 

 the ribs being much larger, ftraiter, more diftant, and 

 covering the whole fhell. Whether it is really the mu- 

 ricata may perhaps be doubted, but we have been induced 

 to follow fo experienced and able a conchologift, not- 

 withftanding the fynonyms of Gmelin and Chemnitz 

 do not accord with ours. In the latter author is a very 

 good figure of our fhell, differing very little from that we 

 were favoured with by the Do6lor, except in being rather 

 more fpinous. 



DIV. 



