There is a saying on Wall Street that industries consolidate at the top of a market and at the bottom.

Consider, if you will, the case of Johnson & Johnson, which is buying Santa Barbara-based Mentor Corp. for $31 per share — or slightly more than $1 billion total. That’s basically a 100 percent premium over the $16 per share Mentor was selling for before the deal became public on Dec. 1.

And it looks like top dollar. But not so fast.

From another perspective, maybe J&J is getting its own version of a Kmart Christmas markdown. It is scooping up the breast implant and cosmetic surgery products company for just 75 percent of the price of Mentor shares at the beginning of the year.

And the New Jersey-based health-care giant is making an all-cash offer, a move likely to forestall a higher competing bid and seal the deal. So what looks like a frothy bid is really a blue light special.

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