ID conundrum - how old is too old?

[paul monfils]

Yes, taxonomy is an ever-changing science.  It is also the most objective and least exact of all the sciences, though it is now gradually becoming more objective through DNA studies.  In a book more than 40 years old, you are bound to find many discrepancies, compared to what is known today about the same organisms.  Many of the tools taxonomists currently use were not available then, and classification was based largely on shell structure, aided by radula studies in some cases.

I took a quick look at your excellent images of your shells.  A couple of comments - The shell you have labeled "Tectus niloticus" is actually Trochus (Tectus) conus, and the Marginella "punum" should be "prunum".

Regards.