6 14 ORDER HETEROTRICHA. 



surface of the body clothed with short, fine, vibratile cilia; contractile 

 vesicle posteriorly located. 



The animalcules of this genus closely resemble those of the Peritrichous genus 

 Strombidium, but are to be distuiguished from them by the fine ciliation of the 

 entire general surface of the body, and which, corresponding with that of Stcntor or 

 Ti?itinniis, necessitates its relegation to the Heterotricha. The only species so far 

 observed is an inhabitant of fresh water. 



Strombidinopsis gyrans, S. K. Pl. XXXI. Fig. 39. 



Animalcule elongate-ovate, about twice as long as broad, the anterior 

 margin truncate, the posterior extremity conical ; cilia of the peristome 

 very strong and powerful, bent outwards, their length equal to that of 

 the entire body, forming a spiral wreath of rather more than one turn, 

 which commences at some little distance from the anterior margin ; its 

 left limb or extremity descending into the oral fossa, which is further con- 

 tinued to the centre of the body as a distinct pharyngeal passage ; cilia of 

 the cuticular surface very fine and short. Length of body 1-350". 



Hab. — Pond water. 



The animalcules forming the t)-pe of this species were met with in a pond con- 

 taining Myriophyllum and other aquatic plants, obtained from the neighbourhood of 

 Stoke Newington, London, in the month of Februar)', 1874. The extremely long 

 outward-bent peristomal cilia, taken together with the ovate form of the body, 

 convey to this species an aspect not unlike that of a miniature shuttlecock. Its 

 movements in the water are extremely vigorous, and difficult to follow, consisting of 

 a_ swift gyratory motion, interrupted by rapid dartings to and fro across the field of 

 view. 



Fam. V. TRICHODINOPSID-ffi, S. K. 



Animalcules free-swimming, persistent in shape, illoricate, posterior 

 border discoidal, acetabuliform, and adherent at will ; oral aperture sub- 

 terminal, approached by a spiral fringe of larger adoral cilia; general 

 cuticular surface finely ciliate throughout. 



Genus L TRICHODINOPSIS, C. & L. 



Animalcules freely movable, of more or less conical outline, having an 

 anterior adoral ciliary system and posterior adhesive sucking-disc, streng- 

 thened with a horny ring, similar to that of Trichodina, but the entire sur- 

 face of the body covered with fine vibratile cilia. Occurring as parasites 

 or commensals upon various aquatic Mollusca. 



Trichodinopsis paradoxa, C. & L. Pl. XXXI. Figs. 39-43. 



Body conical or cap-shaped, slightly curved, gradually tapering from the 

 broadly expanded base to the bluntly pointed anterior extremity ; the 

 posterior sucking-disc occupying about two-thirds only of the diameter of 

 the basal region, slightly eccentric ; ciliary zone surrounding this structure 

 longer and stronger than those of the oral region or general cuticular 

 surface ; interior corneous ring having no denticulations, but spirally striate 



