This is the main bass riff for schism. This is the accurate version, not the one played down on the 3rd and 5th fretts.
Tab by Byron Currier

This uses only the top 2 strings or G and D.
This is the 1st version

G-----------------10----9---------------------10----9----12--
D---0--10--12-------0----0----0--10--12-------0----0-----0
       |_______|__________|_________|_____________|
        triplet         eighths           triplet            eighths

2nd version used throughout the song

G-----------------9----7-----------------------9----7----10
D--0--10--12-------0----0----0--10--12-------0----0----0

Same rhythm as the 1st

This is the 2nd way to play the 2nd version if you wish, but it is not as clean.

G-----------------9-------------------------------9----------10
D--0--10--12-------0-12-0-----0--10--12-------0-12-0------0


The harder riff with heavy distortion guitar that only shows up a few times in the piece is the same as the 1st version but on strings  D and A and slightly longer.
Listen to the recording to get a good sense of feel for the piece and find a drummer to play with you.
The measures are 3/4    4/4 alternate!!!!