e. Mouth at end of long peristome Family _Pleuronemidæ_ running along ventral side; body dorso-ventrally or laterally compressed; left edge of peristome with great, sail- like undulating membrane f. Mouth and pharynx distinct, Family _Isotrichidæ_ posterior; cilia uniform. Parasites in ruminants. g. Mouth absent; body vermiform, Family _Opalinidæ_ cilia uniform. Usually parasites. KEY TO MARINE GENERA OF ENCHELINIDÆ Diagnostic characters: Form ellipsoid or ovoid; the mouth is invariably terminal and is usually round--more rarely slit-formed; it is closed except when food is taken. An oesophagus when present is a short, invariably non-ciliated tube which is usually surrounded by a more or less clearly defined buccal armature. The anus is usually terminal. Large food particles are swallowed, never introduced by currents. 1. Body naked 3 2. Body inclosed in a shell or coat 7 3. a. Cilia uniform about the entire 4 body; body symmetrical b. Cilia in the mouth region 5 longer than the others; body symmetrical c. Bristles, or tentacles, in 6 addition to cilia 4. Mouth terminal; body ellipsoidal Genus _Holophrya_ to ovoid 5. a. Mouth terminal; body elongate, Genus _Chænia_ flexible, and elastic b. Mouth terminal; "neck" highly Genus *_Lacrymaria_ elastic; entire body flexible; conical "head" c. Mouth terminal; "neck" highly Genus *_Trachelocerca_ elastic; entire body flexible; "head" square d. Mouth terminal; "neck" highly Genus _Lagynus_ elastic; no separate mouth-bearing portion 6. a. Body asymmetrical; bristles Genus _Stephanopogon_ in addition to cilia b. Body symmetrical; 4 small Genus *_Mesodinium_ tentacles from mouth; cilia and cirri in girdles 7. Shell composed of small Genus *_Tiarina_ sculptured pieces; cilia long, uniform * Presence at Woods Hole indicated by asterisk. Genus LACRYMARIA Ehr. '30. (Ehrenberg, C. G., 1838; Perty '52; Claparède & Lachmann '58; Stein 59-83; Quennerstedt '66, '67; Fromentel '74; Kent '81; Gruber '84; Gourret & Roeser '86; Bütschli '88; Schewiakoff '89.) Body short to very long flask-shape; for the most part contractile, especially in the neck region. The posterior end is rounded or pointed. The main character is the mouth-bearing apex, which "sets like a cork in the neck of the flask." One or more circles of long cilia at the base of the mouth portion or upon it. The body is spirally striped. Contractile vacuole terminal, with sometimes one or two further forward. Macronucleus central, globular to elongate, sometimes double. Food mainly bacteria. Fresh and salt water.