QUESTION:  Most temples have "Lightning Whelks" on the altar. I have heard from some that this is an accepted exception but I have very serious doubts. Any information about other kinds of sea shells besides conch shells. Maybe you could write a detailed article on the subject sp people could know the truth.

REPLY: Shastra says "bone" is impure, BUT, Conch Shell (Indian Turbinella Pyrum) is super-pure, even to bathe the Deities. Even Lakshmi Devi and Her Lord Narayana carry one in Their hand. Shastra doesn't say ANY SHELL or EVERY SHELL is pure, it's only Indian Shank (Turbinella Pyrum) that is pure. And these come in two types, normal left side opening AND special right side opening (Valampuri Dakshin-varti Turbinella Pyrum). Both are ruled by Goddess Lakshmi. It is not required to have right-side opening. Left side (normal) opening Shank is perfect for puja. And Lakshmi Shank is even better than perfect. It is said by Conchologists that only one Lakshmi Shank is found among 1,000 normal Indian Shanks. And ALL Indian shanks are pure and auspicious.

BUT common Lightning Whelk (busycon contrarium), with no internal formation and no ridges in the conch cavity -  is a bogus non-pure shell.  And as you mention so many temples use this non-conch shell, and they're doing puja with an impure non-conch shell simply because they have been hoodwinked by con men. It is embarrassing that temples use the wrong shell. And in many temples they openly display the fact that they have been cheated on a bogus Conch. And worse, they tell the public that they have a REAL Sri Lakshmi Conch, even though that is untrue.

Fact: The left side opening OR the right side opening Turbinella Pyrum Indian Conch - with 3 to 7 ridges in the conch cavity, and special internal structure is the ONLY Shank that is Vedic. The normal left-side opening Conch is very low price, even less than the bogus ones (Lightning Whelk), and only the Indian Shank is correct for puja.
Genuine Valampuri Lakshmi Shank Turbinella Pyrum Conch shells sell by the gram. Normal size is about 60-120 grams. Depending on quality and number of ridges in the conch cavity they sell for between Rs. 1,000 up to Rs. 3,000 per gram. This means that a genuine Lakshmi Shank can be had for a few thousand dollars ONLY. So no one has any excuse to use a non-conch shell. Everyone can use either a $2 normal Shank OR a $2,000 Lakshmi Shank. BUT, USE A SHANK, ONLY!