The area around Mare Humorum is particularly rich when near the terminator.
Hippalus stands out as an incomplete "ghost crater". To the south,
Doppelmayer and nearby Puiseux are other interesting "ghost craters".
On the western edge of Mare Humorum, Rimae Mersenius and Rupes Liebig
(really on chart 51) stand out prominently.
To the southwest of Gassendi, Rupes Liebig and its extension, Mersenius
rille II, traced a north-south chord across the mare as far south as
Mersenius G. Mersenius II was less distinct, but I could trace Mersenius I
all the way from just north of Mersenius D to about 16 degrees south
latitude. I could not see the complete de Gasparis rille system, just
I and III. This area would be worth looking at with greater aperture
in favorable conditions.
On the far northern edge of Mare Humorum, just northeast of Gassendi,
is an interesting structure standing out in relief against the smooth plain
of the mare. It looks like a trilobite, or perhaps a lobster.
The structure is shown well at the very top of Rukl chart 52,
at 37 degrees west latitude.
Mare Humorum was a particularly interesting area. Doppelmayer
showed a large central peak and--unlike Rukl's drawing--looked to have a
broken concentric ring around the peak. Rukl shows detail to one side of the
peak. The view last night gave the appearance of a broken ring all the way
around. Rimae Doppelmayer was clearly in evidence. Some of Gassendi's rilles
were easily seen, but I was distracted by Doppelmayer, and didn't spend much
time on it.