Strombidium caudatum Fromentel '74. Fig. 46, a, b, c.

Fromentel described a fresh-water form of this genus with a caudal appendage. The body is pyriform, broadly truncate on the anterior end, in the middle of which rises a papilliform process (Schnabel).

On this process is a heap of pigment granules, which, however, are not constant. A ring of long cirri surround the anterior end and pa.s.s into the peristome, and from the left edge of this line of cirri a large adoral zone continues down to the mouth. The peristome is elongate and sac-form, and the mouth lies at the posterior extremity.

With the exception of a caudal filament there are no other motile organs; this is about half as long as the body, structureless, hyaline, and sharply pointed. It splits up into a bundle of fine fibers upon treatment with caustic potash (c). The cirri emerge from minute hollows in the edge of the anterior border. The cortical plasm contains peculiar rod-like bodies, which look more like lines or markings than like rods or trichocysts. The nucleus is large, spherical, and placed in the center of the body. The contractile vacuole is posterior.

Length without appendage is about 35; greatest diameter 15 to 18.

In decaying vegetable matter. Common.

[Ill.u.s.tration: 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; Butschli '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 sh.e.l.l 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 50; greatest diameter 40.

[Ill.u.s.tration: Fig. 47.--_Tintinnopsis beroidea_.]

Var. compressa Daday '87.

The posterior end of the sh.e.l.l is pointed, the lower third of the sh.e.l.l is swollen, the upper third is uniform in diameter and without oral inflation or depression. Nucleus not seen.

Length 70; greatest diameter 48.

Tintinnopsis davidoffi Daday. Fig. 48.

The sh.e.l.l is large, elongated, and provided with a considerable spine. The chitin of the sh.e.l.l is covered with silicious particles of diverse size. The internal structures were not observed.

Length of sh.e.l.l and spine 230; diameter of the oral aperture 54.

[Ill.u.s.tration: Fig. 48.--_Tintinnopsis davidoffi_.]

The variations of these species are considerable, and as the internal structures, such as the nucleus, are essential in fixing their systematic position, I place them as above, provisionally, and until further observations can be made.

KEY TO FAMILIES OF HYPOTRICHIDA.

a. Peristome indistinct; cilia on Family _Peritromidae_ ventral surface uniform and not One genus, *_Peritromus_ differentiated into cirri

b. Peristome more or less indistinct; Family _Oxytrichidae_ cilia reduced to a few rows on the ventral surface; a.n.a.l and frontal cirri present

c. Cilia entirely reduced; frontal Family _Euplotidae_ and a.n.a.l cirri present or reduced; macronucleus band-formed or spherical

d. Peristome reduced to left edge and Family _Aspidiscidae_ does not reach over the anterior One genus, *_Aspidisca_ margin

* Presence at Woods Hole indicated by asterisk.

Genus PERITROMUS Stein '62.

(Stein '62, '67; Maupas '83.)

The body is flat, colorless or tinged with yellow, and contractile.

It is elliptical in outline, with broadly rounded ends; in some cases the left edge is slightly incurved, the right edge convex.

The ventral surface is flat, the dorsal surface is arched in the middle region of the body. The edges being flat are somewhat more transparent than the remainder of the body. The ventral surface is striated by longitudinal straight or slightly curved lines, the dorsal surface is smooth and without cilia. (Maupas describes bristles on the back, but this is not corroborated.) The adoral zone is fairly well developed, but not distinctly marked off from the remaining ventral surface. It begins on the right side and extends entirely around the frontal margin and down the left side below the middle of the body, where it turns suddenly to the right, entering the slightly insunk peristome. The mouth leads into a short, indistinct oesophagus. One contractile vacuole is situated in the dorsal swelling at the posterior end of the animal. Macronucleus double, one in each side of the dorsal swelling. Movement is slow and creeping, with a peculiar method of contracting the more hyaline edge, which may turn upward or around a foreign object.

Fresh (?) and salt water.

Peritromus emmae Stein. Fig. 49.

With the characters of the genus.