Flagellates with one flagellum, a spindle-form body and a high degree of plasticity, the contour constantly changing. A distinct, usually striped cuticle is invariably present. "Eye-spots" are absent. Fresh and salt water. Astasia contorta Duj. Fig. 16. _Astasia inflata_ Duj. '41. The body is colorless, transparent, and flexible. It is largest in the center, thence tapering at the two extremities. The surface of the cuticle is obliquely striated, giving to the animal a distinctly twisted appearance. The contractile vacuole is in the anterior neck-like portion of the body. The flagellum is inserted in a distinct oesophageal tube, into which the contractile vacuole empties. This tube is continued into a deeper pharyngeal apparatus of unknown function. Common in decaying algæ. Length 60µ; greatest diameter 30µ. [Illustration: Fig. 16.--Two aspects of _Astasia contorta_.] Genus ANISONEMA Bütschli Flagellates with two flagella, of which one is directed forwards and is concerned with the locomotion of the animal, while the other is directed backwards and drags after the animal when in motion. Body slightly compressed dorso-ventrally (fig. 17, section). An oral furrow is present on the ventral side and the two flagella originate in it (fig. 17, at left). The vacuole is on the left side. Food vacuoles are present in the posterior part. The nucleus is central. Movement creeping. Fresh and salt water. Anisonema vitrea (Duj.) Fig. 17. Synonyms: _Tropidoscyphus octocostatus_ Stein '83; _Sphenomonas_ Kent '81; _Ploeotia vitrea_ Senn 1900. With the characteristics of the genus. It differs from freshwater forms in having eight furrowed surfaces running somewhat spirally from the posterior to the oral end. Length 50µ; width 23µ. This attractive flagellate was quite common in decaying algæ at Woods Hole; its shaking movement, its peculiar furrowed surfaces, and, above all, its perfectly transparent, vitreous appearance, were well described by Dujardin. Stein's _Tropidoscyphus octocostatus_ is a fresh-water form which may possibly be a distinct species, especially as it is described with both flagella directed forwards. [Illustration: Fig. 17.--_Anisonema vitrea_.] Genus DISTEPHANUS Stöhr. An aberrant flagellate bearing a single flagellum and a silicious skeleton resembling those of the Radiolaria. The skeleton consists of two rings of different diameter parallel with one another and connected by silicious bars. From the wider ring half a dozen bars radiate outwards and a similar number of short thorn-like bars point inwards obliquely. The color is yellow, and except for the flagellum the form might easily be mistaken for a Radiolarian, as has been the case repeatedly. Distephanus speculum Stöhr. _Dictyocha speculum_ Stöhr; _Dictyocha_ Auc. With the characters of the genus.