The area of Mercury around 270° longitude has been observed in 2002 by Leonid Ksanfomality with the 1.29 m telescope of the University of Iraklion, Greece (Link to the PDF version of the paper). On his images, a dark and circular feature is visible, which is interpreted as a double-rim basin of a diameter of 25° or more in longitude. The traditional name for this region of Mercury is Solitudo Aphrodites.
The image above shows cylindrical projection maps of images with a central meridian of approximately 270° which have been contributed by members of the ALPO Mercury Section. The resolution of the images is not much lower than that of Ksanfomality's images. For each map, north is to the top and west to the left, the zero meridian corresponds to the right border, and longitude is increasing from the left to the right. Scale is 1 pixel per degree in longitude and latitude. In each map, the centre of the suspected basin as given by Ksanfomality (270° W, 8° N) is marked by a green cross. It appears that there is something dark and possibly round at that position.
The cylindrical projection maps have been generated with the software MapMaker_Phase.