identify this cable?

I've spent part of this afternoon sorting through my collection of cable, discarding (to my wife's amazement, and very likely to my future regret) things I have too much of (5m lengths of CW1308 phone cable) or will never need (very short lengths of ribbon cable, twinflex, 3-core -- why did I keep *them*?) I've found a DEC cable I can't identify. It's labelled BC99J, and consists of a 40-pin Berg connected to about 2m of black multicore, which goes into a rectangular potted box, about 6" x 3" and about 0.5" thick. Out of the other side of the box is about 4m of the same black multicore, with the end cut off. The label is date-stamped 12/6/78. Anyone know what this is/was? -- Pete Peter Turnbull Network Manager University of York