Greetings from the sandbank.  I have a full grid but am missing one thematic item.  If I am right, It relates to the extra word in 16 across.  Can anyone give me an indication of the answer in which it appears? 
Also is the thematic item in 34 down a three letter or a two letter one - if I am right it could be either?
Long week ahead so , with the help above, I'll carry on to try and find the three other words.  It's a nice puzzle so my thanks to the setter.