The maker is
BRISSON et Cie
The keys are brass, with the salt spoon shape. It is a 10-key clarinet.
Information from Nophachai:
Based on the photos, this clarinet has saltspoon key covers, keys mounted on screw-in pillars. So I think it was made not earlier than 1860 and not later than 1880.
There are few things on this clarinet that can tell us such as; "MAKER" stamped with the maker's mark, the key arrangement, and the H.P (high pitch, A= 452 MHz) - this clarinet was likely made for export to Great Britain's market.
Regarding the market's value, there are several factors make instruments high or low in value; maker's reputation, materials, innovation of the construction/key arrangements or systems, usability etc. Unfortunately, this clarinet falls into a lower value group ~ $50-$70.