796 ORDER HYPOTRICHA. 



covering the entire ventral surface of the body ; no caudal setae. Length 

 1-280". HAB. Pond water and infusions. 



The relatively large size of this animalcule suggests the probability of its being 

 the imperfect or larval form of a species of Euplotes. 



Glaucoma margaritaceum, Ehr. sp. PL. XLV. FIG. 30. 



Body oval, with an emargination or notch on the left-hand side of the 

 posterior border ; contractile vesicle situated posteriorly in close vicinity to 

 this notch, and the oral aperture with its tremulous membrane on the oppo- 

 site or right-hand side of the same region, but a little more forward ; the 

 dorsal surface obliquely or nearly longitudinally grooved or striate; a 

 single long hair-like seta projecting obliquely towards the left from the 

 posterior extremity. Length 1-150x3" to 1-720". HAB. Pond water and 

 infusions. 



This type is identical with the Cydidium margaritaceum of Ehrenberg and the 

 Cinetrochilum margaritaceum of Max Perty. 



GENUS III. MICROTHORAX, Engelmann. 



Animalcules of minute size, free-swimming, more or less oval, flattened, 

 persistent in shape ; the cuticular surface indurated ; the oral aperture 

 debouching upon a small fossa on the left-hand side of the hinder extremity 

 of the ventral surface, associated with a flap-like vibrating membrane ; 

 cilia confined to the ventral surface, most conspicuous at the two extre- 

 mities ; endoplast and contractile vesicle subcentral. 



In general aspect, and in the character of the oral organ with its vibrating 

 membrane, the minute animalcules referred by Engelmann * to this genus so closely 

 resemble those of the genus Glaucoma here treated as developmental conditions only 

 of more highly organized Hypotrichous forms, that their present retention under a 

 separate generic heading must be regarded as provisional. 



Microthorax sulcatus, Eng. PL. XLV. FIG. 37. 



Body oval, depressed, rounded posteriorly, somewhat pointed anteriorly 

 and curved slightly towards the left, the . left border flattened or slightly 

 concave, the right one convex ; the dorsal surface traversed by three deep, 

 widely separated, longitudinal grooves ; oral aperture developed at the 

 posterior extremity, close to the left-hand border ; the cilia longest, and most 

 conspicuous at the two extremities, confined to the ventral surface ; con- 

 tractile vesicle situated a little in advance of the oral fossa ; endoplast 

 ovate, subcentral. Length 1-425". HAB. Fresh water. 



A second species, Microthorax pusillus, Eng., differs from M. sulcatus only in 

 its smaller size, 1-750", and in the absence of the dorsal furrows; it probably 

 represents a younger phase of the same animalcule. The resemblance of this 

 type to the Cinetrochilum margaritaceum of Perty (Glaucoma scintillans, Ehr.) has 

 been already remarked by Wrzesniowski. 



* ' Zeitschrift fiir Wissenschaftliche Zoologie,' Bd. xi., 1862. 



