The classification of the nematodes occurring in the lungs (and related forms) of land mammals has always been one of considerable difficulty, in large part because of the existing very inadequate descriptions of many of the commoner forms. Most systematic helminthologists have followed and amplified the classification adopted by Railliet and Henry in 1907, a system which divided these nematodes into three main groups — those found in the blood-stream (Hæmostrongylus); those found in the larger bronchi (Dictyocaulus, Metastrongylus and Crenosoma); and those found in the minute bronchi and alveoli (Synthetocaulus). While the first two groups contain four well-defined zoological species, an examination of the forms included in the genus Synthetocaulus shews that it consists of a heterogeneous collection of species, which, although possessing a common habitat, are by no means so closely related as has been supposed, and, indeed, belong to several different genera.

Free-living nematodes commonly occur in cultures of fæces, and as Looss (1911) showed years ago they have frequently been mistaken for the developmental stages of parasitic nematodes. For this reason it is important that detailed knowledge of the morphology of such free-living forms should be available. With this end in view the following illustrated account of what appears to be a new genus of nematode has' been prepared. The worms occurred originally in a culture of the fæces of a brown rat, Rattus norvegicus, made for the study of the free-living stages of the Strongyloides of the rat; and as after detailed study it has been found impossible to find any existing description of nematodes which agree with the structural appearances shown by the worms, it has been decided to create a new genus for their reception.

During the pursuit of field work in the neighbourhood of Warwick in which the collection and examination of insects was involved, it was observed whilst carrying out dissections of dung-infesting beetles that several of them had attached to various parts of the exoskeleton collections of what were at first taken to be fungus spores. On close examination, however, these adherent bodies were discovered to be encysted nematodes which were using the beetles as carrying agents, whereby their transference to fresh dung, required for further development, would be assured.

Our attention was drawn to a short note, written by Christie (1925), in which this author discusses the finding of what was either Rhabditis coarctata Leuck. or a closely related species on a number of species of dung beetles in America. With this information in mind, it was decided to culture the worms in order to follow out the life-cycle, determine the species, and make observations on the behaviour of the nematodes in relation to the insects on which they were found attached.

This paper forms a preliminary account of the occurrence of some helminths parasitic in sheep and pigs in South-Eastern England. The rocks of the Wye district are mainly Cretaceous, while Romney Marsh, with its extensive sheep population, is alluvial. Earlier workers have already considered certain helminthic parasites of this region. The present writer uses Morgan's technique. Thirteen helminths parasitic in the gut of sheep and lambs are listed with notes, and a record is made of some other observations, including the identification of Ascaris lumbricoides and Œsophagostomum dentatum from swine.