98 BULLA. 



four divisions, of which the forms are given in the 

 plate of Bulla. Though some, even many of the 

 species might with great propriety be removed to 

 other families, still, as the object is not to alter, 

 but to elucidate, it is trusted that all the shells 

 which can, consistently with the definition, be in- 

 cluded in the genus, and all those which have found 

 admission rather because they do not belong to any 

 other than that they strictly correspond with the 

 character of this Linnsean tribe, will be arranged 

 with facility under one or other of the above-men- 

 tioned sections. 



Many of the Bullae are river shells ; but the ma- 

 rine species are usually imbedded an inch or two 

 below the surface of the sand. The name Bulla, 

 a luhhle, is very descriptive of the swelled round 

 form which characterizes the legitimate offspring 

 of tiiis family, and should exclude those which have 

 been surreptitiously introduced. 



