PLATE LXXII. 



M These smaller ones," says Da Costa, " are the young Shells, 

 but always with them are found old ones of double or treble the 

 size ; in every other respect like these, but proportionally larger and 

 stronger in their several parts and work. The plaits or foldings 

 near the mouth are deep and very strong ; the striae stronger and more 

 distinct ; the border round the mouth greatly turned outwards, very 

 broad, flat, thick, milk white, and the sinuosities, jags or teeth, 

 within, are large, white, and very conspicuous ; some are bidentated, 

 and most of these old ones have eleven, and some even twelve spires, 



" From these circumstances, authors run into confusion, by 

 making the different growths different species. The accurate and 

 judicious Lister himself has formed two species, in his tit. 10. and 11. 

 on the difference of the number of the spires and other slight parti- 

 culars. The several figures in Gualtieri are only varieties ; and the 

 bidens of Linne, Syst. Nat. p. 1240. No. 649. and of Mr. Pennant, 

 Brit. Zool. No. 1 17. tab. 81. fig. 117. is apparently no other than an 

 old Shell, for such large and bidentated ones I have not unfrequently 

 found nestled with these common smaller Shells, 



" Though the number of spires in a Shell is a criterion, yet it is 

 not an infallible one, for the number of spires vary in some species, 

 either from the growths or sexes : in such cases the young Shells have 

 always a less number, and the males have their spires less numerous 

 than the females. This very species is, perhaps, as strong an instance 

 of the difference in the number of the spires as can be, for it is 

 found from six to twelve spires, as Linne has also noted in his 

 Fauna Suecica." 



Linnaeus, and Gmelin in his last Systema Naturae, distinguish the 



