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alized crown of still longer ones at the oral end; they arise outside of the skeletal elements and do not pass between them, as in _Coleps_. KEY TO MARINE GENERA OF TRACHELINIDAE. Diagnostic characters: Body bilateral, or asymmetrical by local prolongations; usually compressed or flattened laterally, the left side more convex than the right. The essential feature is the position and character of the mouth. This is either a long slit extending from the anterior end well down the ventral surface, or the posterior part only of a ventral furrow remains open as a round or elongate mouth some distance from the anterior end. The entire mouth region of the body is usually drawn out into an elongate tapering proboscis which is generally curved dorsally at the extremity. An oesophagus is short or absent altogether; when present it is supported by a stiff buccal armature. Cilia are uniform about entire body or limited to the flat right side. Food is swallowed. 1. a. Proboscis easily distinguished 2 from the main body b. Proboscis not marked off from Genus *_Loxophyllum_ main body; body flat; both surfaces striated 2. a. Mouth runs the entire length Genus _Amphileptus_ of proboscis; entire body uniformly ciliated b. Mouth runs the entire length Genus *_Lionotus_ of proboscis; body flat; right side only is ciliated c. Proboscis much drawn out, Genus _Dileptus_ flexible; mouth at its base * Presence at Woods Hole indicated by asterisk. Genus LOXOPHYLLUM Dujardin '41. (Duj. '41; Wrzesniowski '69; Quennerstedt '65; '67; Cohn '66; Entz '84; Gourret & Roeser '88; Buetschli '88; Shevyakov '96.) The body is flat and somewhat leaf-shape, flexible, and elastic. The anterior end is somewhat proboscis-like and flexible, but is not sharply demarcated as in _Lionotus_. The central portion of the body is developed into a more or less arched dorsal mass, which usually contains the nuclei and contractile vacuoles. As a result of this local thickening, the body is surrounded by a thin hyaline margin. This, however, may be absent on the right side in some species. The mouth reaches from the anterior extremity to a short distance from the end, and usually approaches the left edge. An anus is present near the posterior end of the dorsal swelling. Trichocysts are numerous on the ventral surface, and often on the dorsal surface,
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