OF CONCHOLOGY. 67 



event of danger it immediately with- 

 draws within its cell, and sinks to the 

 bottom. 



Lamarck proposes two distinct ge- 

 nera of the Arffonauta. The first is 

 exempUfied by the iVrgonauta Argo 

 of Linne ; the second is constituted 

 by the Argonauta Vitreus of GmeUn, 

 and he terms it Carinaria-. It is some- 

 what remarkable, that the great Linne 

 should have been completely at a loss 

 where to place this shell ; and in the 

 twelfth edition of the Systema Natu- 

 rae, we find it placed among the Pi^ 

 tillse, under the title of Patella Cristata, 

 to which tribe it bears no resemblance. 

 It was by Gmelin, with more propri- 

 ety placed among the Argonauta; but 

 even in this situation it seems mis- 

 placed, and I concur with Lamarck 

 in the propriety of forming a new 

 genus with it. Lamarck terms it the 

 Carinaria, 



