beachboys2 pointed me to two entries on the ubuntuforum
relating to the same problem. Neither of the two
solutions willl work...
1) one refers to system>sound (does not exist), but
system settings>multimedia reveal usb device 0x46d:089
has been removed (but not forgotten)
2) the second suggests removing pluseaudio! Skype won't
work without pulseaudio since last year.

both these solutions are now 4 years old.

So basically I can't see the webcam microphone.
How do I reinstate the usb device (even though the
camera part does work), and lsusb shows the device.

The webcam in question is a Logitech C210.

Go to Sound Preferences/Settings.

Make sure that in both Hardware & Input the webcam is selected, not built-in audio.

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