In the spring of 1878 my patients returned from China. They had experienced fresh attacks from the parasite; moreover, one of their children, a little girl, was also victimised by the same species of fluke. Thus, in one family I have encountered three cases of fluke-helminthiasis due to _Distoma crassum_! One of the worms passed by the little girl _per anum_ is now in my possession. It not only shows the upper testis perfectly, but also the many times transversely folded, simple, uterine rosette which is certainly not branched. There are also traces of an organ which I take to be the cirrhus-pouch; but I have never seen the penis protruded externally. For the purposes of diagnosis I subjoin the following characters. The _Distoma crassum_ is a large, flat helminth varying from an inch and a half to two and a half inches in length, and having an average breadth of five eighths of an inch; it is especially also characterised by its uniform and considerable thickness, combined with the presence of a double alimentary canal which is not branched; the body is pointed in front, and obtusely rounded posteriorly; the integument being smooth and unarmed; the reproductive orifices placed immediately above the ventral sucker; the testes form two large rounded organs, situated below the uterine rosette, and disposed in the middle line, one in front of the other; the uterine folds occupy the front part of the body; near the lateral margins there are two large vitelligene glands, one on either side of the intestinal tube; the excretory organ probably consists of a central trunk with diverging branches, opening below. BIBLIOGRAPHY (No. 5).--_Budd_, original notice in his ‘Diseases of the Liver,’ 2nd edition, quoted by Lankester in Appendix B to Küchenmeister’s ‘Manual of Parasites,’ p. 437, 1857.--_Cobbold, T. S._, “Synopsis of the _Distomidæ_,” in ‘Journ. of the Proceed. of the Linnean Soc.,’ vol. v, Zool. Div., 1860 (original description p. 5).--_Idem_, ‘Entozoa,’ p. 193, 1864.--_Idem_, “Remarks on the Human Fluke Fauna, with especial reference to recent additions from India and the East,” the ‘Veterinarian,’ April, 1876.--_Idem_, “On the supposed Rarity, Nomenclature, Structure, Affinities, and Source of the large Human Fluke (_D. crassum_),” ‘Linn. Soc. Journ.,’ vol. xii, Zool. Div., 1876, p. 285 _et seq._--_Idem_, “Observations on the large Human Fluke, with notes of two cases in which a missionary and his wife were the victims,” the ‘Veterinarian,’ Feb., 1876.--_Idem_, “The new Human Fluke,” in a letter published in the ‘Lancet,’ Sept., 1875.--_Leidy_, in ‘Proceed. Acad. Nat. Sciences of Philadelphia;’ see also Dr McConnell’s paper quoted below (Bibl. No. 6).--_Leuckart_, l. c., Bd. I, s. 560.--_Weinland_, l. c. (Bibl. No. 2), Appendix, p. 87.