The De La Rue N.B., 'Nota Bene', was introduced in 1895 as a stylographic pen but a fountain pen adaptation was available to purchase separately as an option, as in this 'Dwarf' example. In 1896 De La rue became a limited company and pens were then stamped as 'De La Rue Co. Ltd., this pen is simply 'De La rue'.
The first pen made by De La Rue, in 1881, was the 'Anti-Stylograph' which was very similar to this pen with the nib section fitted as standard. The knurling on the nib section, colour, and design leave no doubt that this was a factory produced product specifically for this pen.
An eyedropper filler, the pen is constructed in hard rubber, there are some marks to the end section of the barrel cap but the pen is in good condition, given its great age.
The original nib would have been by De La Rue but the pen came to me nibless so I found a Parker nib that fits well and writes nicely. I filled the pen to do the test but I don't recommend it as a pen for every day use, the eyedropper is a bit of a faff to fill and then clean out.
At around 130 years old this remarkable and antique pen was made when the fountain pen was in it's infancy. It represents a concrete transition, by De La Rue, from stylographic instruments to the modern fountain pen.