MESOSTOMATIDAE _Byrsophlebs graffii_ Jen. Plymouth, Millport. _B. intermedia_ Grff. Millport, Port Erin. _Proxenetes flabellifer_ Jen. Millport, Plymouth, Port Erin. _P. cochlear_ Grff. Millport. _Otomesostoma._ _Mesostoma productum_ Leuck., _M. lingua_ O. Sch., _M. ehrenbergii_ O. Sch., _M. tetragonum_ O. F. M. (Fig. 19, A). All at Cambridge. _M. rostratum_ Ehr. Widely distributed. _M. viridatum_ M. Sch. Manchester. _M. robertsonii_ Grff., _M. flavidum_ Grff. Both at Millport. _Bothromesostoma personatum_ O. Sch. Preston. _Castrada._ PROBOSCIDAE _Pseudorhynchus bifidus_ M‘Int. Millport, St. Andrews, Port Erin. _Acrorhynchus caledonicus_ Clap. Generally distributed. _Macrorhynchus naegelii_ Köll., _M. croceus_ Fabr. Plymouth, Millport. _M. helgolandicus_ Metsch. West coast. _Gyrator hermaphroditus_ Ehrbg. St. Andrews. Also common in fresh water. _Hyporhynchus armatus_ Jen. Plymouth, Port Erin. _H. penicillatus_ O. Sch. Plymouth. VORTICIDAE _Schultzia._ {50} _Provortex balticus_ M. Sch. Generally distributed. _P. affinis_ Jen., _P. rubrobacillus_ Gamb. Plymouth. _Vortex truncatus_ Ehrbg. Abundant in fresh water. _V. armiger_ O. Sch. Millport (fresh water). _V. schmidtii_ Grff., _V. millportianus_ Grff. Millport. _V. viridis_ M. Sch. Generally distributed. _Jensenia._ _Opistoma._ _Derostoma unipunctatum_ Oe. Edinburgh. _Graffilla._ _Anoplodium._ _Fecampia erythrocephala_ Giard. Plymouth, Port Erin. SOLENOPHARYNGIDAE _Solenopharynx._ ALLOEOCOELA.