Queensland State Archives posted a photo:
Lisbon Lemon trees have more thorns than other lemon tree species. The trees, which will grow up to 8 metres, are somewhat frost hardy.
The lemons are smaller than other lemon species and have thick, smooth skin with barely discernible pits in them. There will be a nipple on the end opposite where the stem was.
Lisbon Lemons are very juicy and quite tart, with few or no seeds. Each lemon will have an average of 10 segments in it.
These lemons are very popular with home gardeners in Australia.
Lisbon Lemons originated in Portugal. They were introduced into Australia by 1824, and into California by 1849.
Description source: Cook’s Info
Image source: Queensland State Archives, Digital Image ID 27246