MARINE PROTOZOA FROM WOODS HOLE. 
481 
the body. The two halves of the body are similar, the posterior being somewhat shorter; the anterior 
half has seven equatorial plates, an oral plate, two lateral apical plates, and one or two dorsal plates. 
The two antapical plates frequently have atooth-like process. The bodies are colorless, green or brown. 
Fresh and salt water. 
Peridinium digitale Pouchet. Fig. 23. 
Synonyms: Protoperidinium digitate Pouchet; Protoperidinium Bergh p.p.: P. divergens Peck. 
The shell is covered with pits of large size. The posterior part is hemispherical and surmounted 
by a single horn or spine. The transverse furrow is very oblique, and its two extremities are united 
by a sigmoid longitudinal furrow. The anterior half bears two spines or horns of different size, and 
variable. The nucleus is spherical or ellipsoidal and placed in the posterior half of the shell. 
Length 68 a; diameter 54 a . Common. 
Although the description of Pouchet’ s P. digitale differs in some respects from a careful description 
of the Woods Hole form, I think the species are the same. The chief difference is in the single horn 
of the posterior half; in Pouchet’s form this is furrowed by a narrow groove which runs to the 
S-sliaped longitudinal furrow. In the Woods Hole form I was unable to make out such a furrow. 
The flagella, also, were not seen. This same form was pictured by Peck ’95 as P. divergens. 
Peridinium divergens Ehr. Fig. 24. 
Synonym: Ceratium divergens Kent. 
The shell is spheroidal, widest centrally, attenuate and pointed posteriorly; the anterior portion 
is armed with two short, pointed horns, each of them having a toothed process at the basal portion of 
the inner margin. They are frequently colorless and beautifully transparent, the body being free 
from large opaque granules; again they are colored brown or yellow. The nucleus is large and 
elongate and finely granular. 75 a long and 68a in diameter. Common. 
Genus CERATIUM (Schrank). 
(Stein ’78; Perty ’52; Clap. & Lach. ’58; Bergh ’82; Pouchet ’83; Gourret & Roeser ’88; Btitschli '85; 
Kent ’81; Senn 1900; Schutt’98.) 
The general shape is a flattened sphere with three long processes or horns. The cross-furrow is 
either spiral or circular; the longitudinal furrow is usually wide and occupies the greater part of the 
