Here is an old post on the flag.
Black Flag of Texas Troops
Posted By: Richard H. Holloway
Date: Saturday, 7 April 2007, at 2:42 a.m.
Black flag carried by Texas troops description.
DAILY CONSTITUTIONALIST [AUGUSTA, GA], July 2, 1861, p. 2, c. 2
Special Correspondence of the Constitutionalist.
Letter from Richmond .
Richmond, Va., June 28, 1860 [sic]
. . . A terrific company of “Texan Rangers” arrived yesterday. They look as if each man could swallow a live Yankee without pinning his ears back. Their flag is of sombre black, embellished with a death’s head and cross bones. It is said they take and receive no quarters, like the celebrated Polish corps of Lutzow’s Wild Hunters. . . .
Gary D. Bray