Earring and Myers—The Rotifers of Wisconsin. 579 
The body is comparatively short and thick-set, the greatest 
width being about one third of the total length. The integument 
is moderately flexible and the outline of the animal quite constant. 
It is one of the most transparent species of the genus and very 
favorable for the study of the internal organs. 
The head and neck are short and broad, and there is a well 
marked transverse fold between the head and neck, as well as one 
between neck and abdomen. The abdomen increases very gradu¬ 
ally in width to a point about two thirds its length and is rounded 
posteriorly. The tail is distinctly marked off from the body; 
it has only a single, median lobe, rounded posteriorly. The foot 
has two joints; the basal joint is broad and short, its length 
barely exceeding that of the tail; the second foot joint is also 
short, but only half the width of the first. The toes are short, 
about one twentieth of the length, conical, slightly blunted at the 
tips, and very slightly decurved. The dorsal and lateral antennae 
are small setigerous pits and in the normal positions. 
The corona extends down on the ventral side about one third 
the length of the body; the post-oral portion forms a fairly 
prominent chin. The auricles are short and stout, with close-set 
robust cilia continuous with the corona. 
The mastax is virgate and appears trilobate in a ventral view 
on account of the muscles attached to the posterior ends of the 
fulcrum and manubria. The trophi are noticeably asymmetric, 
the left side being more strongly developed than the right. The 
fulcrum is long and quite stout, the posterior end being incurved 
and of a Y-shaped section, providing a larger surface for the at¬ 
tachment of the muscles of the piston. The rami appear sub¬ 
square in a ventral view and are bent nearly at a right angle at 
the extreme anterior point. The right ramus has a large basal, 
median projection ending in a blunt tooth; behind this projection 
it is slightly excavate and then inclines gradually towards the 
teeth of the unci. This ventral portion is rather coarsely denticu¬ 
late; beyond the anterior angle the dorsal portions of both rami 
are finely, but distinctly, denticulate. The left ramus has a basal 
projection similar to that of the right, but smaller, and it is more 
deeply excavate in front of the uncus; the ventral denticulation 
is somewhat finer than that of the right ramus. The unci have 
only a single well developed tooth; to this is attached a basal 
plate with a rudimentary tooth close to the main tooth; a diag¬ 
onal rib crosses the uncus from the posterior ventral angle 
