New Peritriclious Infusoria, &c. Bij Br. A. G. Stokes. 481 



Opisthosttjla glolularis, sp. no v., fig. 8. 



Body subglobose, soft and somewhat changeable in shape, often 

 slightly gibbous, the length but little greater than the breadth ; 

 cuticular surface transversely striate; peristome less than the body 

 centre in width, the border revolute ; ciliary disc not elevated ; 

 pedicle slightly exceeding the body in length. Length of body 1/000 

 in. Hab. Pond water, attached to Hydrodidyon utriculatum. 



Opisthostyla similis, sp. nov., fig. 9. 



Body subvasiform, somewhat changeable in shape posteriorly, 

 less than twice as long as broad, somewhat gibbous, slightly con- 

 stricted beneath the revolute peristome border; the posterior region 

 bearing two rounded, transverse annulations, the anterior being the 

 larger, the posterior extremity often apparently united to the pedicle 

 through the intermedium of a disc-like appendage ; cuticular surface 

 strongly striate transversely ; ciliary disc slightly and obliquely 

 elevated ; pedicle in length somewhat exceeding that of the body, the 

 distal extremity scarcely curved ; contracted body obovate, slightly 

 invaginating the extremity of the pedicle. Length of body 1/1125 

 in. Hab. Pond water, attached to the rootlets of various tioating 

 aquatic plants. 



This form is readily recognizable from those previously described, 

 by the presence of the annular body-enlargements, and the slight 

 distal curvature of the pedicle. The backward springing of the 

 contracted zooid is that characteristic of the genus, but individuals are 

 at times met with in which the larger, more anterior annulation lacks 

 the usual convex borders, being replaced by flattened, almost perpen- 

 dicular margins, so that this portion of the body more nearly resembles 

 a short cylindrical constriction. In these individuals the posterior 

 ring is frequently inclosed within that part of the posterior region 

 which invaginates the extremity of the pedicle when the zooid is 

 contracted, the animalcule in these cases appearing not to have 

 extended the body entirely so as to free the pedicle wholly from its 

 invagination, the posterior annulation thus becoming obscure or 

 obsolete. 



Halsis (aXaa, leaping), gen. nov. 



Animalcules free-swimming, ovate, persistent in form, peritrichous ; 

 equatorial ciliary girdles two or more ; several long, non-vibratile, 

 widely separated setae projecting from the posterior body region ; no 

 supplementary spi-inging hairs ; oral aperture terminal, the adoral 

 cilia seeming to form a simple spiral wreath. Inhabiting fresh water. 



Halsis furcata, sp. nov. 



Body ovate, less than twice as long as broad, the posterior 

 border rounded, the anterior convexly truncate ; oral aperture 

 apparently eccentric, surrounded by a short, snout-like projection 



