Recent collection of lung fluke material from hydrophiid sea snakes permits a reevaluation of the suitability of criteria separating the monotypic genera Pulmovermis Coil and Kuntz, 1960 and Hydrophitrema Sandars, 1960. Consideration is also given of the new subfamily Pulmoverminae, erected by Sandars (1961) to include these genera within the digenetic family Hemiuridae. Typographical errors in the original description of H. gigantica Sandars, 1960 have been corrected, reducing the gross or external measurements of that species by ten times. Validity of characters such as flexure of the body, location of testes and ovary with respect to body length, length of seminal vesicle compared to body length, and anterior extension of the seminal vesicle with respect to acetabulum have been rejected. Retained are general body shape, relative position of acetabulum and development of peduncle, degree of coiling of seminal vesicle, and tandem or oblique arrangement of testes. Characters newly employed include body length-to-width ratio and presence of a cuticular fold in Hydrophitrema enclosing both suckers. Retention of the present genera based on these revised characterizations is recommended. Subfamily criteria (form, structure, and size of seminal vesicle, shape of vitellaria) are similar to those employed among the other nineteen subfamilies of this large and possibly heterogeneous group. In addition, these flukes are unique within the family on ecological and physiological grounds, in that they parasitize the lungs of sea snakes rather than the stomach of marine fishes, the usual site and host for members of this family.