Cabinet cards
Cabinet card, def. A photographic print mounted on cardboard approximately 4¼ × 6½ inches.
Introduced in the 1860s, cabinet cards superseded the carte-de-visite. The format was common until about 1900. Early cabinet cards typically used albumen prints, although a variety of other processes were used for later cards. The photograph is usually smaller than the card, leaving approximately a half-inch at the bottom, where the name of the photographer or studio was printed.
Source: Dictionary of Archives Terminology
St. Catharines