1880.] ODD [Stokes. 



as the body. Length of body 7 1q inch. Habitat — Pond-water ; attached 

 to Cypris. 



The contracted body is ovate, and the pedicel is then invaginate within 

 the posterior extremity, this margin of the zooid coming into actual con- 

 tact with surface of the object supporting the pedicel. 



The characteristic conical form of the ciliary disk, either alone or in 

 connection with the invagination of the pedicel by the contracted body, 

 renders the species readily distinguishable from all other members of the 

 genus. 



Opisthostyla, gen. nov. (0-mjOz • a~u)>oq). 



Animalcules resembling those of Rhabdostyla, but the rigid pedicel 

 curved near its point of attachment to the submerged object, this part 

 acting, when the zooid is contracted, like a spring, and throwing the 

 animalcule and the otherwise inflexible foot-stalk backward through the 

 water, the whole immediately becoming upright by the recoil of the 

 curved extremity of the pedicel. Inhabiting fresh water. 



Opisthostyla annulata, sp. nov. (Figs. 12, 13). 



Body conical campanulate, slightly changeable in form, somewhat gib- 

 bous or the lateral margins nearly straight, the zooid obliquely or verti- 

 cally placed on the pedicel, less than twice as long as broad, strongly 

 striate or annulate transversely; obovate when contracted; peristome 

 border revolute, ciliary circles two ; pedicel as long as the body, the distal 

 extremity suddenly and shortly curved. Body and pedicel each yyV- inch 

 long. Habitat — Pond-water ; attached to Algse. 



The short curve at the end of the pedicel at its point of attachment to 

 the supporting object seems to act as a spring, as already stated, to assist 

 the zooid in throwing itself backward when the body contracts, the entire 

 Infusorian then describing rather more than a semicircle in the water, 

 having the point of attachment of the foot-stalk as the centre. The move- 

 ment is usually very quickly accomplished, the return of the animalcule 

 to its normally erect position being almost as suddenly achieved. 



In the "Annals and Magazine of Natural History " for February, 1886, 

 the writer described an Infusorian under the name Rhabdostyla pusilla, 

 which is certainly a member of the new generic group here formulated. 

 The following is an amended diagnosis of the form referred to : 



Opisthostyla pusilla Stokes (Rhabdostyla pusilla Stokes *). 



Body campanulate, tapering posteriorly, less than twice as long as 

 broad, the surface transversely striate ; peristome slightly exceeding the 

 body-centre in width, the border revolute ; contracted zooid ovate ; pedi- 

 cel scarcely longer than the body, the distal extremity shortly and sud- 

 denly curved. Length of body TT \ 5 inch. Habitat — Pond-water ; at- 

 tached to Ceratophyllum. 



* Annals and Magazine of Natural History, S 5, Vol. xvii, p. 108, PI. I, Fig. 17. 



