[PD] newbie, Mac OS X: problem with (certain) missing(?) GEM objects

[michael doser]

Just started using GEM and PD, and while I am exploring GEM, it seems to
me that certain objects for pixel manipulation that are listed as 
existing
(pix_convolve, pix_motionblur, ...) are missing in my setup (the 
terminal
window puts up a error message, and the object itself has no 
connectors),
while other objects work fine (pix_kaleidoscope, pix_aging,...). I am
sure that the answer is trivial, but for the while being, I'm rather 
stuck..

thanks - michael