486 THE AMERICAN NATURALIST. [VoL. XXXIII. 
long, vibratile flagellum produced from the anterior extremity; contractile 
vesicle indistinctly developed. Inhabiting fresh water. 
M. PLOSSLII PERTY. 
Body ovate or elliptical, slightly narrower anteriorly, cuticular surface 
finely shagreened or crenulate, thickly clothed with fine hair-like setæ, whose 
length is less than that of the body ; flagellum long and slender, retractile ; 
endoplasm vacuolar, amber color or greenish-yellow ; contractile vesicle 
indistinct, EE located. Length of body, 1-1000” to 1-900”. Habitat 
marsh water 
This description is somewhat incomplete and does not take 
into account certain common variations from the type form. 
Examination of a large number of specimens found in the 
waters of Massachusetts and New York has revend the fol- 
lowing facts : 
The length of Mallomonas varies at different times and in 
different localities from 20 to 6op. The ratio of length to 
width varies from 4 to 1. Sometimes the bodies are long and 
narrow, and sometimes they are almost spherical, resembling 
the Rhizopod, Actinophrys. The older forms are somewhat 
more spherical than the younger ones. All forms of Mallomo- 
nas are more or less spherical in end view. 
The setz or spines vary in length from 15m to 30m; the 
average length is about 25m. They have a diameter of 0.3 at 
the base and taper to a point at the fore end. They are gener- 
ally straight, but, being flexible, they sometimes appear to be 
curved. At the base they bend sharply like a polo stick and 
are attached to basal plates which have a rectangular shape. 
It is the irregular lapping of these basal plates that produces 
the corrugated appearance of the cuticular surface mentioned in 
Kent’s description. The setæ are easily broken off, and it is 
not uncommon to see specimens with only two or three setæ 
present. When the organism moves forward the setæ are 
directed backwards. 
The color of the organism is usually green when the specimen 
is young and fresh, but sometimes it changes to greenish-yel- 
low or brown. Besides the two chromatophores, a contractile 
vacuole and numerous oil globules may be discerned. The 
