24.in-addr.arpa has never been delegated.
What do you mean? Address space has been assigned by ARIN:
whois -h whois.arin.net 24.128
Continental Cablevision - North East (NETBLK-CVSN-CCNE) CVSN-CCNE
24.128.0.0 - 24.128.255.255
There appear to be registered nameservers for some blocks. And just now:
set type=soa
24.in-addr.arpa.
Server: starship.av8.com
Address: 198.3.136.10
IN-ADDR.ARPA
origin = A.ROOT-SERVERS.NET
mail addr = hostmaster.INTERNIC.NET
serial = 1999010400
--Dean