pg_hba.conf and groups

I am trying to allow individuals within a PostgreSQL (v7.4) group to
connect to the backend. The relevant line in pg_hba.conf is (I
believe):

host <db> +<group> <IP address>/32 md5

Note that I have replaced the contents of the real fields with <...>,
but that these match across what follows. I understand the + to allow
access to members of the group.

The contents of the system catalogs include the following:

# select * from pg_catalog.pg_shadow;
usename | usesysid | usecreatedb | usesuper | usecatupd | passwd | valuntil | useconfig
-------------+----------+-------------+----------+-----------+--------+----------+-----------
<name> | 105 | f | f | f | md5... | |

# select * from pg_catalog.pg_group;
groname | grosysid | grolist
---------+----------+-----------------------
<group> | 100 | {100,101,102,104,105}

Nevertheless, the following command fails:

psql --host <dbhost> --dbname=<db> --username=<name>
psql: FATAL: no pg_hba.conf entry for host "<IP address>", user "<name>", database "<db>", SSL off

Have I set this up incorrectly? Is there any way to query the backend
in order to identify who it thinks has access to what?

Thanks for your help.

Cheers,
Brook