OP CONCHOLOGY. 135 



ticularly the outer lip, wliicli is frequently, on this account, 

 broken, the very light color in the quite young, and the ab- 

 sence of callosity upon the columella. 



A comparison of shape, angle of divergence of the whorls, 

 &c., with specimens of adult shells, or with figures and de- 

 scriptions, will generally suffice to detect half-grown shells. 



Many of the ponderous Alabama Goniohases are bulbous 

 in the half-grown state; the spire at first narrowly acuminate, 

 then suddenly and very convexly expanding, resembling the 

 growth of certain West India Gylindrellse. As with these 

 terrestrials, the subulate portion invariably disappears in the 

 adult, leaving a somewhat papseform shell. 



We thus find that no one character (with very few excep- 

 tions) can be relied on in specific discrimination, but rather a 

 combination of characters, with a general idea of the necessary 

 allowance for variation pervading other species of the same 

 general type, or contiguous locality. 



