WM & S plated fish knife and fork set

Hi and thanks in advance for your time and for sharing your knowledge

I have a 6 person fish knife and fork set that I have been trying to identify.  I found a mark that seems to indicate they are William Marples & Sons  of Sheffield however, I have  not been able to find any references or samples of fish kinves mande by them as they were took makers.  

So, either they dabbled in tableware or I have the wrong maker.  Another possibilty is that they are by William Moulton of the US , but that seems  less likely I think.

Can anybody help with identifying these items and their era. I'd also like to know  what the handles are made of?  Bone??

again  thanks for your help.

Chleo