38 Transactions of the Society. 



border ; nucleus long, band-like, transversely placed close to the anterior 

 extremity. Length of body 1/450 in. Habitat, standing pond water. 



The movements are extremely rapid and erratic, the animalcule 

 darting through the water by revolution on the longitudinal axis so 

 rapidly as to defy examination. Fortunately, however, it has the habit 

 of temporarily attaching itself to some supporting object by means of its 

 posterior extremity, when it becomes comparatively quiescent ; but even 

 then it rotates on its long axis. At other times it swings to and fro 

 in the field, describing a long curved path through the water as though 

 it were attached to the end of a restraining but invisible thread. 



This infusorian may readily be distinguished from all other known 

 species of the genus by the long, band-like nucleus, an organ of this 

 form not having been recorded as belonging to any previously described 

 Stromhidium. 



I have not been able to positively demonstrate the presence of two 

 contractile vesicles. The creature's movements are so rapid and erratic, 

 that the study is difficult under any circumstances, but to observe a 

 small, laterally developed pulsating vacuole while the infusorian is 

 rotating and continually carrying the organ beyond the focus, is well 

 nigh impossible. The posteriorly located vesicle is large and seen with 

 comparative ease. 



Mesodinium finibriatum sp. nov., fig. 13. 



Body divided into two unequal, subglobose regions by a transverse 

 groove, from which springs the girdle of setose cilia, each of these 

 appendages being distally cut into three or more unequal branches; 

 cuticular surface obliquely and finely striate, so that the margins of the 

 body, when examined from either extremity, present a crenulated outline ; 

 contractile vesicle large, spherical, located at one side near the posterior 

 extremity. Length of body 1/1125 in. Habitat, standing pond water. 

 Movements rapidly rotatory, with frequent lateral leaps. 



The distinctly fimbriated condition of the locomotive cilia at once 

 separate this from all previously known species. 



In company with this interesting form there was present a Meso- 

 dinium corresponding in all essential characters with M. jndex C. & L., 

 a species hitherto recorded from salt water alone. The only noticeable 

 difi"erence was in the size, the fresh-water variety being somewhat larger 

 than the marine. The cilia of M. pulex are not fimbriated. 



Pysjcidium vernale sp. nov., fig. 14. 



Body elongate vasiform, twice as long as broad, consisting of a 

 subcentral, subspherical region suddenly constricted anteriorly to produce 

 a short, neck-like prolongation, and lengthened posteriorly to form a 

 portion tapering to the pedicle and constituting about one-third of the 

 entire length of the zooid ; peristome border crenulate ; ciliary disc large, 

 considerably and obliquely exserted, bearing three ciliary circles ; vesti- 

 bulum extending to near the body-centre ; cuticular surface finely striate 



