The family Gnathostomidae contains several genera and a fair number of species of nematodes of rather aberrant type and of uncertain affinities. As pointed out by Baylis and Lane (1920) in their excellent revision of the family, there is little doubt but that it should be included in the superfamily Spiruroidea. The subfamily Gnathostominae is characterised by the possession of a head bulb containing four closed membranous hollow structures, called ballonets by Baylis and Lane, connected posteriorly with four elongate sac-like structures designated cervical sacs. Three genera are recognised in this sub-family as follows: Tanqua, in which the head bulb is provided with transverse cuticular ridges, and Echinocephalus and Gnathostoma in which the head bulb is provided with rows of thorn-like spines. In Echinocephalus the body is smooth and destitute of cuticular spines, whereas in Gnathostoma all or a large part of the body has rows of cuticular spines on the posterior edges of the annulations. The first two genera are parasitic in the intestinal tract of cold-blooded vertebrates, whereas Gnathostoma apparently has its normal habitat in the stomach wall of mammals, as Baylis and Lane have pointed out.