Below I have provided the Katakana spelling for Janemba as provided by Daizenshuu 6. Now when you break it up into it's parts, you find that not everything adds up. Either I translated this wrong, but if I'm not mistaken the fourth character in the word is the Katakana character "so".

The only conclusion I have is that I simply translated it incorrectly. Otherwise it had occured to me that if you replace "so" (ソ) with "me" (メ) then it would make sense (romanized would be Janemeba). However I find this unlikey because in Daizenshuu 6 it is clearly written as "so" (ソ). Unless they messed and wrote his name wrong throughout the entire book...
