Issue extracting my snortrules

[Akinwale Fasuru <fashman2k1 () yahoo com>]

Hello,
 Please I need help extracting my snort rules with this command 
# tar -xzvf snortrules-2931.tar.gz
I get this erro message 

zip: stdin: not in gzip format

tar: Child returned status 1

tar: Error is not recoverable: exiting now
 
I downloaded the file with this command # # wget
http://www.snort.org/sub-rules/snortrules-snapshot-
2923.tar.gz/<oinkcode> -O snortrules-2931.tar.gz 
I put in the oinkcode
I have tried to re-safe the file with extension .tar and issue the same command leaving out z but still it wont work. 
PLS HELP!

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