OF EVOLUTION. 91 



fossil ; on the other hand, the nodose ribs of 

 the fossil frequently tend in the direction of 

 tuberculation, thus again bridging the interval 

 between the two species. We have step by step 

 all the intervening gaps filled in between the 

 two species, and in such a manner as to leave no 

 doubt concerning the interrelationship of the 

 forms in question. It is interesting to note in this 

 connection that no individuals of the recent 

 form occur in the deposits containing the fossil 

 species, which, as an inhabitant of the seas 

 immediately preceding the present one, may 

 very reasonably be looked upon as the imme- 

 diate progenitor of the stromb of the modern 

 Gulf. 



In the case of the other two forms which I 

 have brought before you, the fossil crown-conch 

 (Melongena subcoronata) and volute (Valuta 

 Floridand), we have similar or analogous details 

 of structure which unite them with their living 

 representatives (Melongena corona, Voluta Junonid). 

 Thus, the first-named is distinguished from the 



