Hi Petra, l understand what they are for, l just haven't seen any with splits before. As you say AuntieE they may be purely decorative but l think they may slip over epaulettes,
The split collar is a very distinctive ecru colour and l have a scarf and handkerchief that match it, l think they may be silk.
When l bought my current house l inadvertently bought the contents, belonging to the previous owner, an very well to do 90 year old spinster.
I actually feel some responsibility for various articles from her life, which is why l don't just want to discard the lace items, I do not think the collars would have been hers, but probably one of her family.
There are far newer ones, plain linen, bought from Broadbents in Southport (department store, I've researched it). They aren't so interesting. I shall see if l can find a clothing museum that might be interested in them.
I also have many pairs of vintage gloves, far too small for modern day hands but some exquisitely made.