Host not found

Unable to find a host corresponding to the IP address 131.111.226.204.
The output of `dig -x '131.111.226.204'` follows:

; <<>> DiG 9.3.6-P1-RedHat-9.3.6-4.P1.el5_4.2 <<>> -x 131.111.226.204
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 35246
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:
;204.226.111.131.in-addr.arpa.	IN	PTR

;; AUTHORITY SECTION:
111.131.in-addr.arpa.	14400	IN	SOA	authdns0.csx.cam.ac.uk. hostmaster.ucs.cam.ac.uk. 1283975898 14400 3600 604800 900

;; Query time: 3 msec
;; SERVER: 83.166.160.10#53(83.166.160.10)
;; WHEN: Thu Sep  9 12:34:48 2010
;; MSG SIZE  rcvd: 119