That is the adapter card for connection to a 5080 graphics system.  See
page 2-47 and 2-48 in manual at
http://ohlandl.ipv7.net/6152/RT_PC_User_Setup_Guide.pdf
The 5080 system was a high performance graphics processor originally
hosted by 370 systems but adapters where made to host them on RTs and
later on RS/6000.
Paul
On 2017-04-03 5:56 AM, Mattis Lind via cctalk wrote:
  This card is sitting in a IBM RT PC.
 
http://i.imgur.com/Adqnxr3.jpg?1
 What kind of card is it? The WD1935 seems to be a SDLC chip. I cannot find
 any reference to the numbers P/N 6247874 (bottom layer etch) or the number
 on the sticker on the backside: 6247871G001
 It is connected to an IBM marked dongle which has 4 BNC connectors.
 Is it a 3278-3279 emulation board?
 /Mattis