Although Fromentel's species is incompletely described, it is very evident that the organism corresponds fairly well with the Woods Hole variety. His was a fresh-water type; this is marine, but the caudal filament and the contractile vacuole are similar. Certainly in this case the organism can not be regarded as a Vorticella broken off its stalk, as Kent '81 suspected. The anterior process with its pigment spot; the cirri, the spherical nucleus, the position of the vacuole, etc., are all opposed to such an interpretation which Kent applied to the original species. Neither can it be a Tintinnoid. I place it provisionally as _S. caudatum_. KEY TO THE MARINE GENERA OF TINTINNIDÆ. Diagnostic characters: Body attached by a stalk to a cup. Inside the zone of membranelles is a ring of cilia (par-oral). 1. The test is gelatinous and more or Genus _Tintinnidium_ less covered by foreign particles 2. The test is chitinous and clear. Genus _Tintinnus_ No foreign particles. 3. The test is chitinous; covered by Genus *_Tintinnopsis_ foreign particles, growth rings frequent 4. The test is chitinous, often Genus _Codonella_ covered by foreign particles. The test is marked by discoid, circular, or hexagonal spots. 5. The test is perforated by pores Genus _Dictyocysta_ of circular or hexagonal form. * Presence at Woods Hole indicated by asterisk. Genus TINTINNOPSIS Stein '67. (Stein '67; Kent '81; Daday '87; Bütschli '88.) Medium-sized ciliates, inclosed in a chitinous lorica with embedded sand crystals. The form of the house, or lorica, varies greatly. In some cases the mouth opening is wide, giving the lorica a bell form; it may be long and tubular, short and spherical, or variously indented. The animal is attached, as in the closely allied genus _Tintinnus_, by a peduncle to the bottom of the lorica. The anterior end of the animal is inclosed by two complete circles of cilia; one, the outer, forming the adoral zone, is composed of thick tentacle-like membranelles, the other consists of shorter cilia within the adoral zone. The mouth leads into a curved oesophagus containing rows of downward-directed cilia (Daday). The entire body is covered with cilia, but as the lorica is always opaque these can be made out only when the animal is induced to leave the house. The only difference between this genus and _Tintinnus_ is the covering of foreign bodies--usually sand crystals. Movement is rapid and restless, and peculiarly vibratory, owing to the apparent awkwardness in moving the house. Salt water. Tintinnopsis beroidea Stein, var. plagiostoma Daday. Fig. 47. Synonym: _Codonella beroidea_ Entz '84. The shell is colorless, thimble-shaped, with a broadly rounded posterior end. The body is cylindrical. The internal organs were not observed. Membranelles 24 in number. Length 50µ; greatest diameter 40µ. [Illustration: Fig. 47.--_Tintinnopsis beroidea_.] Var. compressa Daday '87.