(Kent '81; Bütschli '86; Klebs '97; Senn 1900.) The body is small, globular or oval and either free-swimming or fastened by one of the two flagella. The body is sometimes a little amoeboid, with short pseudopodial processes. In addition to the main flagellum, there are usually one or two small flagella at the basis of the larger one. The nucleus is usually anterior, and one or two contractile vacuoles are present. Monas sp. Fig. 9. An extremely small form (3µ) attached by a thread of protoplasm--perhaps a flagellum, to algæ. The body is ovoid and the main flagellum is about four times the length of the body. The contractile vacuole is posterior. Only one specimen was seen and upon this I shall not attempt to name the species. [Illustration: Fig. 9.--_Monas_ sp.] Genus MONOSIGA Kent '81. (Bütschli '86; Francé '97; Senn 1900.) Small colorless forms of Choanoflagellida, always naked and solitary. The posterior end is attached directly to the substratum, or there is a short stalk not exceeding the body in length. Kent '81 distinguished nine species, but Bütschli questioned the accuracy of many of these, and in this he was followed by Francé '97, who recognized three species--_Monosiga ovata_, _M. fusiformis_, and _M. augustata_. Fresh and salt water. Monosiga ovata S. Kent '81. Fig. 10. Synonyms: _M. brevipes_ S. K.; _M. consociata_ S. K.; _M. limnobia_ Stokes. The individuals are unstalked or provided with a very short stalk less than the body in length. The form is spherical or ovate, broadest at the base and tapering to the extremity. The collar is somewhat variable in size. In the Woods Hole forms it was about the length of the body. Oil particles present. Contractile vacuole posterior, nucleus anterior. Fresh and salt water. Length of body without the collar 5µ. [Illustration: Fig.10.--_Monosiga ovata_.] Monosiga fusiformis S. K. Fig. 11. Synonyms: _M. steinii_ S. K.; _M. longicollis_ S. K. The individuals are unstalked, minute, and of a general flask-shape. The body is swollen centrally and tapers slightly at each end. There is no stalk, the body being fixed by the attenuate posterior end. There are two contractile vacuoles and one nucleus, which is situated a little above the body center. Fresh and salt water. Length without collar 9µ; length of collar 3µ. [Illustration: Fig. 11.--_M. fusiformis_.] Genus CODONOSIGA (Jas. Clark '67). (Bütschli '78; Kent '81; Francé '97; Senn 1900.) This genus, as modified by Francé, is distinguished from the preceding by the possession of an unbranched stalk much longer than the body length. The body is naked and of various shapes, and the individuals are solitary or colonial upon a single stalk. Kent '81 enumerates no less than 10 species, which were cut down by Bütschli to 1. Francé admits 4--_C. botrytis_ Jas. Clark; _C. grossularia_; _C. pyriformis_, and _C. furcata_, all S. Kent--but regards the second and third as merely form varieties of the first.