Foreign function call

Let me get more specific. I think it this can be answered then I can translate the information to other calls. In the arima 'R' code there is a reference to

.Call(R_TSconv, a, b)

If from the console I type:

.Call(R_TSConv, c(1,-1), c(1,-1))

I get:

Error: object "R_TSConv" not found

If I do

getNativeSymbolInfo("R_TSConv")

I get:

Error in FUN("R_TSConv"[[1L]], ...) : no such symbol R_TSConv

What am I missing?

Thank you.

Kevin