Delegating Part Of Class C?

[buffalo at icarus.yml.com]

Greetings,

We are using BIND version 8.x. Recently, a large ISP delegated part of a
class C to us:

xxx.xxx.xxx.80 through xxx.xxx.xxx.94

However, when I check the ISP's name servers to see how they delegated the
IPs to us, I notice that while they are pointing all inquiries to our
nameservers, they seem to be doing so strangely. When I try to do a
reverse lookup on one of the delegated IPs on their nameservers, I get:

> 82.xxx.xxx.xxx.in-addr.arpa
Server:  delegating.isp.nameserver
Address:  xxx.xxx.xxx.xxx

Non-authoritative answer:
82.xxx.xxx.xxx.in-addr.arpa     canonical name =
82.80.xxx.xxx.xxx.in-addr.arpa

Authoritative answers can be found from:
80.xxx.xxx.xxx.in-addr.arpa     nameserver = our.primary.nameserver
80.xxx.xxx.xxx..in-addr.arpa     nameserver = our.secondary.nameserver
our.primary.nameserver      internet address = xxx.xxx.xxx.xxx

It appears to me that they are pointing to a record on my nameserver:

db.xxx.xxx.xxx.80

However, if I try to create db.xxx.xxx.xxx.80 on my nameserver, and then
do a reverse lookup on say: 

xxx.xxx.xxx.82, 

my nameserver interprets this as doing a lookup on:

xxx.xxx.xxx.80.82

which obviously doesn't work. If I try to set up the the db record as:

db.xxx.xxx.xxx

on my nameserver, lookups on my nameserver work. However, no matter how I
set it up, lookups from outside nameserver don't work.

Should the delegating ISP just have delegated the IPs to us without
specifying a db file on our nameservers, or should they have done so, but
named the db differently?

Many thanks in advance for any and all responses,

--Duncan