OP CONCHOLOGY. 65 



widening from the top, which is nar- 

 row and pointed, to the base which is 

 wide and extended. 



In Turton's Linne eighteen species 

 of Pinnae are described ; and three 

 onl)' have been found to inhabit the 

 British seas. 



ORDER THIRD. 



TTNIVALTE SHELLS 



With a regular Spire. 



Genus ISth.-ARGONAUTA. Ani- 

 i)ial a Sepia or Clio ; shell univalve, 

 spiral, involute, membranaceous, and 

 unilocular, or consisting of a single 

 apartment or cell. Zdnn Syst. 317. 

 Plate 7th, ^g. 18th. 



Habitation. The Argonautse have 

 only been found to inhabit the ocean, 



K 



