THE WHEEL ANIMALCULES (ROTATORIA) 587 



KEY TO NORTH AMERICAN FRESH-WATER ROTATORIA 



i (138) One ovary. Do not creep like a leech. 



Subclass Monogononta . . 2 



This subclass includes all the rotifers commonly met, save the Bdelloida (q.v.), which are 

 distinguishable by their habit of creeping like leeches. 



2 (109) Corona of various types. Where there are two wreaths of cilia, those 

 of outer wreath never shorter than those of inner. ... 3 



3 (97) Mouth not near center of corona. . . . Order Notommatida . . 4 



Free-swimming or creeping rotifers, but never creeping like a leech; corona ventral or ter- 

 minal, consisting of a disk which is either uniformly ciliate or has a wreath of cilia about its 

 circumference with usually two or more groups of cilia close to the mouth, or shows some inter- 

 mediate condition. Where there are two wreaths of cilia, the outer is never shorter than the 

 inner. Mouth not in the center of the disk. Jaws never ramate (Fig. 867, A) nor malleo- 

 ramate (Fig. 866). Foot usually ending in two toes placed side by side; rarely ending in one; 

 sometimes absent; never forming a disk for attachment nor ending in a bunch of cilia. Lorica 

 present or absent. 



4 (9) Jaws not incudate. Intestine and anus present 5 



5 (31, 64) Without lorica. Corona when as broad as other parts of the body, 

 not consisting of an outer wreath, a partial wreath about 

 the mouth and styligerous prominences between. 



Suborder Notommatina . . 6 



Body usually soft and somewhat segmented. (See also family HYDATINEDAE, 66.) 



6 (26) Corona without long antenna-like bristles and setigerous prominences. 

 Foot present. ..... Family NOTOMMATIDAE . . 7 



Soft-bodied rotifers, usually elongated, cuticula more or less distinctly segmented; foot not 

 distinctly marked off from the remainder of the body, usually short and ending in two toes 

 placed side by side, or rarely but one toe. Corona usually not so wide as the remainder of the 

 body. Living mainly amid vegetation of the shores and bottom. 



This family cannot be sharply marked off from others; see particularly Hydatinidae. The 

 genera of the Notpmmatidae are likewise hot sharply definable; they are merely more or less 

 convenient subdivisions of a group that would be too unwieldy if taken as a unit. 



7 (19) Without auricles 8 



N.B. Auricles are often contracted and are then invisible. 



8 (16) With one or more eyes 9 



9(12,15) With a single eye only. ' 10 



