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 1-1500" to 1-720". Hab. — Pond water and 

 infusions. 



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

 Cinctrochilum margaritaceum of Max Perty. 



Genus IIL 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 de\-elopmental 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 Cinctrochilum margaritaceum of Perty {Glaucoma scintillans, Ehr) has 

 been already remarked by Wrzesniowski. 



' Zeitschrift fur W issenschaftliche Zoologie,' Bd. xi., 1862. 



