Usually SDA trades between 1 & 2 million volume per day but...

Usually SDA trades between 1 & 2 million volume per day but today, there has already been 31.7 Million "traded" !!!

The offending transaction it appears, occurred at 8.54am this morning for a "Special Cross Trade" of 31.2 mill at $5.45

Can anyone explain to this mere mortal retail holder who/why/what this pre-market transaction is ? I know sometimes some instos do crossed trades which they like to call "internal account transfers" but surely a $170 Million transaction deserves to have some disclosure notification ?