greatest diameter 15 to 18 mu.
In decaying vegetable matter. Common.

[Illustration: Fig. 46.--_Strombidium caudatum_.]

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 TINTINNIDAE.

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; Buetschli '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 whe