340 Illinois State Labor'atory of Natural History. 

 Rhabdostyla Kent. 



Similar to Ejpistylis, but not forming colonies. 



Several undetermined species of this genus were found on 

 various Entomostraea, on a rotifer {Polyarthra platyptera)^ 

 and on small aquatic worms. 



Opebcularia Goldf. 



Forming colonies as in Ejnstylis, individuals more or 

 less narrowed at the anterior end, peristome not laterally- 

 expanded; adoral disc very strongly elevated, while the sur- 

 rounding peristomal ring is deeply excavated and the vesti- 

 bule conspicuously wide and very deep ; the adoral disc is 

 therefore borne upon a column, on which it is usually 

 obliquely placed, looking like a ciliated lid to the anterior end. 



86. O. nutans Ehrbg. 



Found in May on a I'lanurbis from Quiver Lake at C. 



87. O. rugosa Kell. ('84). 



Common among vegetation ; a few found in bottom towing 

 in Quiver Lake. Observed in May and July in the river and 

 in Quiver and Thompson's Lakes. This is a line species, and 

 can be easily recognized by its thick pedicel and sessile 

 zooids. Schewiakoff ('93) marks the species with an interro- 

 gation point, but I see no reason for it. 



88. O. irritabilis Hempel ('96). 



This fine large species was found at a variety of places 

 from May to July, during which time it was common and 

 aften abundant, always occurring attached to the surface of 

 some animal, especially young musk-turtles [Aroinochclys 

 udoratus). It was also found upon the backs of snapping 

 turtles {Chelydra scrjx'ntina), and on two kinds of crayfishes, 

 Camharus dloycncs and C. hlandiugii acutns. Its food consists 

 partly of diatoms and Englena. 



The species is similar to Opercularia articidata Ehrbg., but 

 differs from it in the shape of the body, the character of the 

 peristome border and pharynx, and the elevation of the 

 ciliary disc. 



