This typelay is the Caxa baxa shown by Juan Joseph Sigüenza y Vera: Mecanismo del arte de la Imprenta (1811), reprinted Almarabu 1992. The companion upper case is Caxa alta.
The empty case is . Note that there are effectively 3 rows of boxes, unlike U.K. and U.S. cases, which have 3½ rows. The case is partitioned down the middle into a left and right bay.