This paper is the twelfth installment of the present series presenting the data concerning monogenetic trematodes collected during the years 1951-1954 at the Alligator Harbor Marine Laboratory of Florida State University. It comprises an emendation of the family Gastrocotylidae Price,
1943 and the subfamily Gastrocotylinae Sproston, 1946 and descriptions and/or discussions of several species. The new genera Scomberocotyle and Neothoracocotyle have been diagnosed with Scomberocotyle scomberomori (Koratha, 1955) n. comb. and Neothoracocotyle coryphenae
(Yamaguti, 1938) n. comb., respectively as their type species. Emendations have been made in Gotocotyla Ishii, 1933, Thoracocotyle MacCallum, 1913, and Lithidocotyle Sproston, 1946. Pseudaxine mexicana Meserve, 1938, Lithidocotyle acanthophallus (MacCallum
and MacCallum, 1913) Sproston 1946, Gotocotyla elegatis Meserve, 1938, Neothoracocotyle acanthocybii (Meserve, 1938) n. comb., and Thoracocotyle crocea MacCallum, 1913 have been treated. T. paradoxica has been reduced to synonymy with T. crocea. In addition
several notes concerning host-specificity, zoogeography, speciation and other biological facets have been presented.
The Bulletin of Marine Science is dedicated to the dissemination of high quality research from the world's oceans. All aspects of marine science are treated by the Bulletin of Marine Science, including papers in marine biology, biological oceanography, fisheries, marine affairs, applied marine physics, marine geology and geophysics, marine and atmospheric chemistry, and meteorology and physical oceanography.