Here's something to check also, the D7 could stand for 7th Congressional District

U.S., Civil War Draft Registrations Records, 1863-1865 about James M Hughes
Name: James M Hughes
Residence: Harrison, Missouri
Class: All
Congressional District: 7th
Age on 1 July 1863: 30
Estimated Birth Year: abt 1833
Race: White
Marital Status: Married
Place of Birth: Illinois

Source Information:
Ancestry.com. U.S., Civil War Draft Registrations Records, 1863-1865 [database on-line]. Provo, UT, USA: Ancestry.com Operations, Inc., 2010.
Original data:
Consolidated Lists of Civil War Draft Registrations, 1863-1865. NM-65, entry 172, 620 volumes. ARC ID: 4213514. Records of the Provost Marshal General’s Bureau (Civil War), Record Group 110. National Archives, Washington D.C