Just took a look at the numbers, precisely the same issue as last week:
Total 24 hour volume according to CMC is 56 BTC $13,833:

and the total 24 hour volume on the only exchange trading BANX/BTC is 11.36 BTC $ 2783:
https://banx.io/trade?c=BANX&p=BTC83875 Buy 0.00671000 107.00000000 0.71797000 Jun 23, 2015 8:33 PM
83870 Buy 0.00671000 136.00000000 0.91256000 Jun 23, 2015 6:58 PM
83857 Buy 0.00671000 63.00000000 0.42273000 Jun 23, 2015 5:29 PM
83856 Buy 0.00671000 107.00000000 0.71797000 Jun 23, 2015 4:23 PM
83848 Buy 0.00671000 88.00000000 0.59048000 Jun 23, 2015 2:59 PM
83832 Buy 0.00671000 58.00000000 0.38918000 Jun 23, 2015 1:49 PM
83830 Buy 0.00671000 83.00000000 0.55693000 Jun 23, 2015 12:32 PM
83827 Buy 0.00671000 78.00000000 0.52338000 Jun 23, 2015 11:00 AM
83826 Buy 0.00671000 87.00000000 0.58377000 Jun 23, 2015 9:49 AM
83818 Buy 0.00671000 74.00000000 0.49654000 Jun 23, 2015 8:32 AM
83813 Buy 0.00671000 115.00000000 0.77165000 Jun 23, 2015 7:22 AM
83812 Buy 0.00671000 64.00000000 0.42944000 Jun 23, 2015 6:03 AM
83808 Buy 0.00671000 63.00000000 0.42273000 Jun 23, 2015 4:32 AM
83804 Buy 0.00671000 99.00000000 0.66429000 Jun 23, 2015 3:02 AM
83803 Buy 0.00671000 121.00000000 0.81191000 Jun 23, 2015 1:53 AM
83801 Buy 0.00671000 61.00000000 0.40931000 Jun 23, 2015 12:52 AM
83798 Buy 0.00671000 148.00000000 0.99308000 Jun 22, 2015 11:52 PM
83795 Buy 0.00671000 132.00000000 0.88572000 Jun 22, 2015 10:34 PM
83788 Buy 0.00671000 96.00000000 0.64416000 Jun 22, 2015 9:02 PM
The above numbers are pulled directly from Banx.io trade history, btw.
I'd still love to hear an explanation for this, even if it's as simple as "Oh, Banx.io doesn't actually show the full trade history, mate"
Anyone ? I've seen enough BS in this topic so far, so lets just figure out the numbers first before we draw any conclusions.