A metal conversation tube similar in appearance to a flexible monaural stethoscope.
A second example which blurs the boundaries between what was used as a stethoscope and a listening device. See this article. The mouthpiece is unusual being of a convoluted rather than a simple horn type and is constructed from light, strong metal which is I think Aluminium finished with a black lacquer. The tube itself is made from a coil of metal which retains flexibility. There is an extension to the mouthpiece with a larger flange and with this attachment is would have been more suitable as a conversation tube. The date referred in the above article is 1850, again this 19th century example may be later.