BDELLOID ROTIFERA OF SOUTH AFRICA. 59 



collar. The wheels are very shallow and practically circular in 

 shape, and the rims bearing the cilia form complete circles except 

 for the gap over the sulcus, which is very small owing to the 

 slight depth (dorsal to ventral) of the sulcus. The sulcus (right 

 to left) is wide and the bottom boundary of it is a sharp, thin 

 ridge. 



When the animal is feeding, the head is placidly swayed up 

 and down and round about, each great wheel with its vibrant 

 cilia flashing out brilliantly, in varying shades of yellow, as the 

 incidence of the light changes ; now a circle, now some form of an 

 ellipse. The effect is heightened by the lifting or screwing up, 

 at times, of the outside boundaries of the wheels farthest from 

 the sulcus, bringing them more towards the position facing each 

 other, and foreshortening the view of the wheel. The cilia flash 

 in great waves, and the whole effect is most striking and 

 beautiful. When viewed from above, the discs give almost 

 the best representation of two revolving wheels of any species. 



Slight prominences on each disc bear two long setae. On 

 account of the shallowness of the corona, the borders of the 

 upper lip are very flat. The lateral borders have to rise very 

 little from the collar to reach above the sulcus bridge. There 

 they bend round at sharp angles between which the anterior 

 border sags a little, so as to be slightly concave. The sulcus 

 ridge, with its ends elbowing up into the discs, often shows 

 over the upper lip, almost parallel. 



Brushes of scrubby setae protrude from the long antenna. Two 

 eye-spots, very distinct, are seated on the brain mass, which is of 

 an inverted pear shape, well defined, but very small for such a 

 large animal. Jaws of medium size, and rather square in outline, 

 show on each side three large and clearly defined teeth and one 

 smaller, not greatly larger than the striae, but whose point can 

 be distinctly made out. Jaws and borders are often stained 

 deep yellow. 



The rostrum is stout and has a double lamella. From the 

 posterior of the rostrum back to the end of the trunk, the width 

 is practically uniform when creeping ; there is just a gentle 

 inward curve between the antenna and mastax. No swelling is 

 visible in the lumbar region, its outline tapers gently into the foot, 

 and this tapering is continued down to the spurs. At the ankle 

 there is a slight sudden narrowing. The outside edges of the spurg 



