If/When they sign a contract

I thought Pryce and Mellor were here on a one-month loan.

[urlhttp://news.bbc.co.uk/sport1/hi/rugby_league/super_league/london/9373302.stm[/url

They are. Calderwood and Latus aren't though. Pryce has been rubbish by the sounds of things so that explains him not being picked, no need for Mellor at the moment.

Thanks for explanation, then wouldnt it be worth getting them on short-term contracts?

True, I should have referred to triallists/loanees (if that's the right expression).
Another possible explanation for their absence is an administrative cock-up, like Mackay and Blanchard each thinking the other was sorting it.