PLAGIOSTOMATIDAE _Acmostoma._ _Plagiostoma dioicum_ Metsch., _P. elongatum_ Gamb., _P. pseudomaculatum_ Gamb., _P. sagitta_ Ulj., _P. caudatum_ Lev., _P. siphonophorum_ O. Sch., _P. ochroleucum_ Grff. All at Plymouth. _P. sulphureum_ Grff. Port Erin. _P. vittatum_ F. and Leuck. Millport, Plymouth, Port Erin. _P. koreni_ Jen. Plymouth, Millport. _P. girardi_ O. Sch. Plymouth, Port Erin, Valencia. _Vorticeros auriculatum_ O. F. M. (Fig. 19, C). Port Erin, Plymouth. _V. luteum_ Grff. Plymouth. _Enterostoma austriacum_ Grff. Plymouth, Port Erin. _E. fingalianum_ Clap. Skye, Plymouth. _E. coecum_ Grff. Millport. _Allostoma pallidum_ van Ben. Millport. _Cylindrostoma 4-oculatum_ Leuck. Skye, Millport, Plymouth. _C. inerme_ Hall, _C. elongatum_ Lev. Plymouth. _Monoophorum striatum_ Grff. Plymouth. BOTHRIOPLANIDAE _Bothrioplana._ _Bothrioplana_ sp.? Manchester. _Otoplana._ MONOTIDAE _Monotus lineatus_ O. F. M., _M. fuscus_ Oe. (Fig. 19, D). Both common littoral forms. _M. albus_ Lev. Plymouth. _Automolos unipunctatus_ Oe. Skye, St. Andrews, Plymouth. _A. horridus_ Gamb., _A. ophiocephalus_ O. Sch. Plymouth. {51}CHAPTER II TREMATODA CHARACTERS OF TREMATODES—HABITS AND STRUCTURE OF TREMATODA ECTOPARASITICA (MONOGENEA)—LIFE-HISTORIES OF _POLYSTOMUM INTEGERRIMUM_, _DIPLOZOON PARADOXUM_, AND _GYRODACTYLUS ELEGANS_—TREMATODA ENDOPARASITICA (DIGENEA)—OCCURRENCE AND HABITS OF DIGENEA—LIFE-HISTORY OF _DISTOMUM MACROSTOMUM_—_DISTOMUM HEPATICUM_ AND ITS EFFECTS—_BILHARZIA HAEMATOBIA_—BISEXUAL TREMATODES—TABLE OF HOSTS—CLASSIFICATION. From the Turbellaria we now pass on to a consideration of the second great subdivision of the Platyhelminthes, the Trematodes or "flukes," of which the "liver-fluke" is the best known, since it is one of the most dangerous parasites that infest domestic animals.