Extended HD partition is listed in fstab and has an /mnt entry, see /mnt/hda4 below:
# /etc/fstab
proc            /proc        proc    defaults          0       0
sysfs           /sys         sysfs   defaults          0       0
devpts          /dev/pts     devpts  defaults          0       0
tmpfs           /dev/shm     tmpfs   defaults          0       0
/dev/hda        /mnt/hda        auto     noauto,users,exec    0 0 # Added by TC
/dev/hda1       /mnt/hda1       ext3     noauto,users,exec,relatime 0 0 # Added by TC
/dev/hda2       /mnt/hda2       ext3     noauto,users,exec,relatime 0 0 # Added by TC
/dev/hda3       none            swap     defaults             0 0 # Added by TC
/dev/hda4       /mnt/hda4       auto     noauto,users,exec    0 0 # Added by TC
/dev/hda5       /mnt/hda5       ext3     noauto,users,exec,relatime 0 0 # Added by TC
Doesn't harm, but definitely not needed and can be misleading.
/dev/hda like entry was already discussed in the summer; Curaga (if I remember well) had a comment on certain badly partitioned MP3 players which can't be mounted on a usual way as /dev/sda1 only as /dev/sda However it is rare exception, would be better to remove these entries too.