516 Wisconsin Academy of Sciences, Arts, and Letters, 
Genus TYLOTROCHA Harring and Myers. 
Notommatid rotifers with spindle-shaped, illoricate body, with 
a distinct constriction between the head and abdomen; two lateral, 
knoblike, retractile processes near mid-length; the tail is rudi¬ 
mentary, the foot fairly long and unjointed; the toe is single, 
formed by the fusion of two originally separate toes. The dorsal 
antenna is double. 
The corona is slightly oblique and has a marginal row of mod¬ 
erately long cilia and two lateral, auricle-like tufts of long cilia; 
the buccal field is sparsely ciliated; on the apical plate are two 
unciliated, retractile elevations without definite form. 
The mastax is a specialized form of the virgate type; all the 
normal elements are fused into a dome-shaped structure, serving 
for the support of the walls of the mastax during the pumping 
action. 
At the posterior end of the ganglion is a lenticular pigment 
body, which is probably a rudimentary retrocerebral sac enclosing 
the eyespot. 
Type of the genus.—Tylotrocha monopus (Jennings) = Notom- 
mat a monopus Jennings. 
TYLOTROCHA MONOPUS (Jennings). 
Plate XXXVII, figures 5-8. 
Notommata monopus Jennings, Bull. Michigan Fish Comm., No. 3, 1894, 
p. 14, figs. 5, 6; No. 6, 1896, p. 87. 
Tylotrocha monopus Harking and Myers, Trans. Wisconsin Acad. Sci., vol. 
20, 1922, p. 555. 
The body of this peculiar species is spindle-shaped and slender; 
its greatest width is about one fourth of the total length. The 
integument is very flexible and the outline varies constantly in re¬ 
sponse to the contractions of the animal. The entire body is of a 
brilliant, translucent reddish-purple or crimson color. 
The head and abdomen are separated by a shallow constriction; 
there is no distinct transverse fold. The head segment decreases 
slightly in width towards the neck; its length is nearly equal to 
the width. The abdomen is fusiform, largest in the middle and 
tapering to the rudimentary tail. Near the middle are two knob¬ 
like lateral elevations, retractile at the will of the animal and con¬ 
stantly changing in form. The foot is relatively long and conical, 
continuing the outline of the body; it is without joints, but deeply 
