Technical caveat: I am assuming this is a simple monoalphabetic homophonic substitution cipher, and not something much harder like a transposition cipher or a polyalphabetic substitution cipher. The only reason I am assuming this is because the first 3-part cipher Zodiac sent to the newspaper was solved using homophonic substitution with a single alphabet (to see this, click the "Switch to 408 cipher" link above, and click the decoder named "The correct one").

Click here to view a high-resolution image of the 340 cipher.

Click here to read the Zodiac Ciphers wiki, a new repository of information related to the Zodiac ciphers.