Agree with davo but i would still say to small but thats just my opinion lol..... 5x3x2 as davo says would be IMO the smallest you would want to go if you was to have one
you maybe ok with a scobina for some time in a 4x2x2
the bigger the tank the better but scobina and som reticulata stay fairly small
scobina max out at about 12 inch disk but are very hard to find im thinking of starting a scobina breeding project as not many people sell them but i wont have any pups for 2 years