Miss C. Smith
Simple imprints, square corners and thin mounts are characteristic of the earliest CDVs like the one on the left. The photo on the right is mounted on a thicker card with a rounded, beveled gilt edge (beyond the capabilities of my scanner). Both were taken by Miss C. Smith, who operated her studio in Lowell, Massachusetts on Merrimack Street over a period of years from the1860's to 70's.
The later cabinet card on the left bears yet another Miss C. Smith imprint. Her studio is now located at 75 Middlesex Street in Lowell and she has acquired a painted backdrop.