82 DAVENPORT ACADEMY OF SCIENCES. 



The species is a common one in pond water and often produced 

 in great numbers in infusions. In general appearance and habits 

 this species resembles Calceolus cypripedmm J-Clark; the latter, 

 however, does not possess two distinct ciliary girdles. 



In movement Urocentnivi tubro proceeds in a direct course, rol- 

 ling on its longitudinal axis, or swiftly darts from side to side, 

 often dragging after it a mass of debris which has adhered to its 

 caudal appendage. 



Reproduction is by transverse division. 



Family, MICROTHORACID^. 



MICROTHORAX Engelmann. 



Somewhat oval, flattened, the dorsal surface grooved, the ven- 

 tral ciliated. Oral aperture in the posterior border on the left 

 side, provided with an undulating membrane. 



MiCROTHORAX SULCATUS Eng. 



Body oval, flattened ventrally, convex dorsally. The dorsal 

 surface with three longitudinal grooves. Cilia on the ventral sur- 

 face only. Nucleus spherical, central. Contractile vesicle pos- 

 terior to the nucleus. 



Length, 40 microns. (Fig. 134, PI. XVII.) 



A very common species in this state. Found nearly everywhere 

 in pond water, associated with Cinetochihwi margaritaceuvi. 



Reproduction is by transverse division. 



The species observed in this state is much smaller than that 

 reported by Engelmann. 



CINETOCHII.UM Perty. 



Oval, flattened, dorsal surface furrowed in a spiral manner. 

 Mouth and contractile vesicle posterior, opposite, the former with 

 a distinct vibratile membrane. Cilia on the ventral surface, uni- 

 form, with a number of hair-like setae projecting obliquely from 

 the posterior region. 



C1NETOCHII.UM MARGARITACEUM Ehr. 



Body broadly oval when viewed dorsally, flattened, with a con- 

 cavity in the posterior border on the left side. Oral aperture in 

 the posterior region on the right side of the concavity and pro- 



