Hey Ranjeev,  Good question - and I bet that nobody really knows!  The problem arises that because of the often severe Ca limits to growth, the snails are probably constrained most of their short lives - so it might appear as indeterminate in a Ca-rich habitat, or determinate in a less Ca-rich environment.  Sorry that I cannot provide an easy answer - but that is the nature of the beast!  Good luck! 

Dear Dr. Bickford,

Thank you very much. That would make distinguishing between adults and juveniles of fossils really complicated.