104 Dr. A. C. Stokes on some 



vesicle single, spherical, postero-lateral, often leaving several 

 small vacuoles after systole ; nucleus single, subcentral. 

 Length of body -^(j inch. 



Hab. An infusion of decaying aquatic vegetation. 



In form this resembles C. cucuUits (Schrank), S. K., being 

 somewhat more curved anteriorly. It differs in liaving but 

 one nucleus, and in the postero-lateral position of the pul- 

 sating vacuole. Reproduction is by transverse fission. 



DiPLOMASTAX, gen. nov. 



Animalcules free-swimming, holotrichous, elongate-ovate, 

 subcylindrical, produced posteriorly in a more or less retrac- 

 tile tail-like prolongation ; oral aperture ventral, enclosing- 

 two vibratile membranes; contractile vesicle single; tricho- 

 cysts absent. 



The proper position of the genus is probably with the Ophryo- 

 glenidse of Kent, although the presence of two vibratile mem- 

 branes will necessitate a slight change in the diagnosis of the 

 family as now formulated. 



Dijjlomastax fronfata, sp. nov. (PI. I. figs. 13 and 14.) 



Body elongate-obovate, subcylindrical, transparent, longi- 

 tudinally striate, and finely reticulated, five times as long as 

 broad, the lower or ventral surface convex, the dorsal slightly 

 concave, tapering posteriorly to a somewhat retractile tail-like 

 prolongation forming about one fifth of the entire body ; an- 

 terior extremity narrowed, obtusely pointed ; oral aperture 

 narrow, ovate, obliquely placed on the ventral or convex 

 surface at some distance from the anterior extremity, enclosing 

 two small vibratile membranes ; contractile vesicle single, 

 spherical, near the centre of the dorsal or concave border ; 

 nucleus presumably represented by a large, ovate, subcentral, 

 clear space. Length of body pg-g- inch. 



Hab. Still water, with Alyriophi/Ilum. 



The aspect of this interesting Infusorian floating on the 

 concave or dorsal surface, with the obliquely placed oral 

 aperture thus directed upwards, at once suggests the thought 

 of a microscopic shark — the suggestion and the resemblance 

 not being far-fetched. It is the appearance, however, that 

 brings the shark to mind. 



Reproduction is accomplished by transverse fission, pre- 

 sumably after conjugation, which I have observed, union being 

 made at the anterior portions of the ventral surfaces. When 

 fission is about to take place that part of the body in advance 



