Roster of Confederate Soldiers, 1861-1865 doesn't list a JOSEPH EVANS with the TX 31st Cav but does list:

Evans, Joseph TX 24th Cav. Co.A Cpl.
Evans, Joseph E. TX 15th Cav. Co.F
Evans, Joseph H. TX Cav. 3rd (Yager's) Bn. Co.D Cpl.
Evans, Joseph W. TX 34th Cav. Co.A

and

Evans, C.O. TX 31st Cav. Co.E

is the only Evans listed with the 31st.