792 ORDER HYPOTRICHA. 



setae exceedingly long, the frontal series placed further back ; caudal setae 

 equalling half the body in length, flexible and trailing, not branched or 

 fimbriate at their extremities. Inhabiting fresh water. 



Fam. VI. ETJPLOTID^E, Ehr. 



Animalcules free-swimming, encuirassed, more or less ovate, with a 

 plane ventral and convex dorsal surface ; oral aperture ventral, situated at 

 the posterior extremity of an arcuate or subtriangular peristome-field, the 

 outer or left-hand border of the peristome bearing a linear series of stout 

 cirrose adoral cilia, shorter cilia of the same description sometimes con- 

 tinued up the reflected or right-hand border of the peristome ; anal styles 

 always present, those of the frontal and ventral series more or less con- 

 spicuously developed, also occasionally a few postero-marginal or caudal, but 

 never a continuous series of latero-marginal setae. 



Excepting for the absence of latero-marginal setas, and the difficulty experienced 

 in discriminating between the groups of frontal and ventral styles, the members of 

 this family group correspond closely with those of the Oxytrichidae last described. 

 The peristomal system is also simpler, for while in some instances it possesses a 

 reflected inner border with an associated fringe of pre-oral cilia, no instance is as 

 yet known in which either an endoral or paroral series is represented. At the same 

 time, this little family group exhibits in certain points an advance upon that of the 

 Oxytrichidae, the cilia of the ventral aspect being more concentrated, and their 

 constituent elements being in all instances highly differentiated in the form of 

 styles and uncini. In the Oxytrichidae, on the other hand, the last-named appendages 

 may, as in Kerona and Trichogaster, take the form of minute setose cilia, and thus 

 lead the way through Peritromus and Litonotus to the more simply organized 

 Holotricha. By Stein the four genera here assembled under the title of the Euplo- 

 tidaa are divided into the two family groups of the Euplotina and Aspidiscina, the 

 second one being instituted for the reception only of the single genus Aspidisca. 

 As this type differs from the three other genera only in the more rearward location 

 of the peristome-field and consequent non-projection of the adoral fringe of cilia 

 beyond the anterior border, it has not been considered desirable to retain this dis- 

 tinction in the present volume. The indurated and more or less ovate or orbicular 

 carapace or cuirass of the members of this family group, combined with their truly 

 ambulatory mode of progress over the surface of submerged objects by aid of their 

 frontal and ventral styles, imparts to many of them an insect-like appearance. The 

 passage from the preceding family of the Oxytrichidae is possibly accomplished through 

 the genus Uronychia, in which two rudimentary, latero-marginal setae are found 

 developed on each side in close contiguity to the anal styles. 



GENUS I. ASPIDISCA, Ehrenberg. 



Animalcules free-swimming, encuirassed, orbicular or shield-shaped, 

 with a convex dorsal and plane ventral surface, the right-hand border of 

 the ventral surface having a thickened margin ; peristome-field set far back 

 on the left-hand side, associated with a simple arcuate fringe of adoral 

 cirri, which do not project beyond the anterior or left lateral margin ; 

 several large claw-like styles usually developed towards the anterior end and 

 in the centre of the ventral region, and from five to ten or twelve posterior 

 or anal styles ; anal aperture placed far back, debouching a little in advance 

 of the posterior or anal styles. Mostly inhabiting salt water. 



