The 9th Mississippi is one of my ancestral units, and I have looked into its history. Ferguson's Brigade, of which it was a part, was attached to Wheeler's Cavalry and countered Sherman during the march to the sea. In an excerpt of Ferguson's memoirs which I read, Ferguson recorded that he crossed the Savannah River, and was ordered to leave his horses in the Carolinas and cross back to the city on foot. He claimed his men did not like leaving their horses, and for humor, when they marched into town, he gave cavalry commands, such as halt, dismount, etc., as if his men were still on horses. He recalled his men got a laugh out of it, and their spirits improved. Ferguson also noted, "My command was sent out in small detachments all along the lines, to points that were weakest, so I really had nothing particular to do.” So perhaps Lt. Richards was killed while the unit was acting as infantry in the lines. When the unit retreated accross the Savannah, it was re-united with its horses.